Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $184.63   10.535%   $204.0808   $204.08   $204.10   $204.10  
  Purchase #2 $177.86   11.255%   $197.8781   $197.88   $197.90   $197.90  
  Purchase #3 $148.51   3.170%   $153.2178   $153.22   $153.20   $153.20  
  Purchase #4 $246.59   5.816%   $260.9317   $260.93   $260.95   $260.90  
  Purchase #5 $102.60   4.429%   $107.1442   $107.14   $107.15   $107.10  
  Purchase #6 $226.96   12.370%   $255.035   $255.04   $255.05   $255.00  
  Purchase #7 $185.53   10.801%   $205.5691   $205.57   $205.55   $205.60  
  7 purchase totals = $1,272.68       $1,383.8567   $1,383.86   $1,383.90   $1,383.80