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 $216.98   3.722%   $225.056   $225.06   $225.05   $225.10  
  Purchase #2 $191.55   5.275%   $201.6543   $201.65   $201.65   $201.70  
  Purchase #3 $34.26   8.814%   $37.2797   $37.28   $37.30   $37.30  
  Purchase #4 $88.90   8.859%   $96.7757   $96.78   $96.80   $96.80  
  Purchase #5 $159.83   4.748%   $167.4187   $167.42   $167.40   $167.40  
  Purchase #6 $51.78   3.170%   $53.4214   $53.42   $53.40   $53.40  
  Purchase #7 $48.70   10.576%   $53.8505   $53.85   $53.85   $53.90  
  7 purchase totals = $792.00       $835.4563   $835.46   $835.45   $835.60