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 $214.77   4.871%   $225.2314   $225.23   $225.25   $225.20  
  Purchase #2 $22.87   13.235%   $25.8968   $25.90   $25.90   $25.90  
  Purchase #3 $101.90   4.213%   $106.193   $106.19   $106.20   $106.20  
  Purchase #4 $91.43   8.399%   $99.1092   $99.11   $99.10   $99.10  
  Purchase #5 $119.84   4.692%   $125.4629   $125.46   $125.45   $125.50  
  Purchase #6 $244.68   10.270%   $269.8086   $269.81   $269.80   $269.80  
  Purchase #7 $153.86   11.770%   $171.9693   $171.97   $171.95   $172.00  
  7 purchase totals = $949.35       $1,023.6712   $1,023.67   $1,023.65   $1,023.70