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 $71.47   7.262%   $76.6602   $76.66   $76.65   $76.70  
  Purchase #2 $201.34   9.743%   $220.9566   $220.96   $220.95   $221.00  
  Purchase #3 $204.72   13.388%   $232.1279   $232.13   $232.15   $232.10  
  Purchase #4 $13.38   11.205%   $14.8792   $14.88   $14.90   $14.90  
  Purchase #5 $173.69   3.225%   $179.2915   $179.29   $179.30   $179.30  
  Purchase #6 $115.29   7.109%   $123.486   $123.49   $123.50   $123.50  
  Purchase #7 $245.34   9.299%   $268.1542   $268.15   $268.15   $268.20  
  7 purchase totals = $1,025.23       $1,115.5556   $1,115.56   $1,115.60   $1,115.70