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 $63.27   9.194%   $69.087   $69.09   $69.10   $69.10  
  Purchase #2 $181.61   7.373%   $195.0001   $195.00   $195.00   $195.00  
  Purchase #3 $154.79   9.675%   $169.7659   $169.77   $169.75   $169.80  
  Purchase #4 $153.99   10.821%   $170.6533   $170.65   $170.65   $170.70  
  Purchase #5 $50.89   11.134%   $56.5561   $56.56   $56.55   $56.60  
  Purchase #6 $102.31   10.704%   $113.2613   $113.26   $113.25   $113.30  
  Purchase #7 $62.28   3.508%   $64.4648   $64.46   $64.45   $64.50  
  7 purchase totals = $769.14       $838.7885   $838.79   $838.75   $839.00