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 $80.94   8.764%   $88.0336   $88.03   $88.05   $88.00  
  Purchase #2 $210.35   6.650%   $224.3383   $224.34   $224.35   $224.30  
  Purchase #3 $46.72   5.670%   $49.369   $49.37   $49.35   $49.40  
  Purchase #4 $33.70   7.597%   $36.2602   $36.26   $36.25   $36.30  
  Purchase #5 $165.83   7.170%   $177.72   $177.72   $177.70   $177.70  
  Purchase #6 $9.75   12.587%   $10.9772   $10.98   $11.00   $11.00  
  Purchase #7 $184.82   11.221%   $205.5587   $205.56   $205.55   $205.60  
  7 purchase totals = $732.11       $792.2570   $792.26   $792.25   $792.30