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 $70.55   7.213%   $75.6388   $75.64   $75.65   $75.60  
  Purchase #2 $108.40   13.399%   $122.9245   $122.92   $122.90   $122.90  
  Purchase #3 $194.31   8.652%   $211.1217   $211.12   $211.10   $211.10  
  Purchase #4 $104.43   12.799%   $117.796   $117.80   $117.80   $117.80  
  Purchase #5 $232.43   7.266%   $249.3184   $249.32   $249.30   $249.30  
  Purchase #6 $96.30   7.626%   $103.6438   $103.64   $103.65   $103.60  
  Purchase #7 $154.59   11.768%   $172.7822   $172.78   $172.80   $172.80  
  7 purchase totals = $961.01       $1,053.2254   $1,053.22   $1,053.20   $1,053.10