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 $221.84   11.694%   $247.782   $247.78   $247.80   $247.80  
  Purchase #2 $178.90   3.747%   $185.6034   $185.60   $185.60   $185.60  
  Purchase #3 $246.46   4.467%   $257.4694   $257.47   $257.45   $257.50  
  Purchase #4 $205.93   7.596%   $221.5724   $221.57   $221.55   $221.60  
  Purchase #5 $220.98   3.857%   $229.5032   $229.50   $229.50   $229.50  
  Purchase #6 $11.29   10.860%   $12.5161   $12.52   $12.50   $12.50  
  Purchase #7 $182.59   10.190%   $201.1959   $201.20   $201.20   $201.20  
  7 purchase totals = $1,267.99       $1,355.6424   $1,355.64   $1,355.60   $1,355.70