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 $49.33   7.391%   $52.976   $52.98   $53.00   $53.00  
  Purchase #2 $184.47   11.133%   $205.007   $205.01   $205.00   $205.00  
  Purchase #3 $176.63   11.692%   $197.2816   $197.28   $197.30   $197.30  
  Purchase #4 $231.84   6.115%   $246.017   $246.02   $246.00   $246.00  
  Purchase #5 $40.80   7.580%   $43.8926   $43.89   $43.90   $43.90  
  Purchase #6 $40.32   4.783%   $42.2485   $42.25   $42.25   $42.20  
  Purchase #7 $91.94   4.139%   $95.7454   $95.75   $95.75   $95.70  
  7 purchase totals = $815.33       $883.1681   $883.18   $883.20   $883.10