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 $89.33   6.325%   $94.9801   $94.98   $95.00   $95.00  
  Purchase #2 $92.90   9.837%   $102.0386   $102.04   $102.05   $102.00  
  Purchase #3 $132.45   9.836%   $145.4778   $145.48   $145.50   $145.50  
  Purchase #4 $155.88   4.732%   $163.2562   $163.26   $163.25   $163.30  
  Purchase #5 $145.56   4.431%   $152.0098   $152.01   $152.00   $152.00  
  Purchase #6 $167.95   6.132%   $178.2487   $178.25   $178.25   $178.20  
  Purchase #7 $55.95   3.678%   $58.0078   $58.01   $58.00   $58.00  
  7 purchase totals = $840.02       $894.0190   $894.03   $894.05   $894.00