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 $145.83   3.142%   $150.412   $150.41   $150.40   $150.40  
  Purchase #2 $240.99   10.514%   $266.3277   $266.33   $266.35   $266.30  
  Purchase #3 $53.85   7.634%   $57.9609   $57.96   $57.95   $58.00  
  Purchase #4 $169.48   6.360%   $180.2589   $180.26   $180.25   $180.30  
  Purchase #5 $208.62   8.853%   $227.0891   $227.09   $227.10   $227.10  
  Purchase #6 $179.68   13.206%   $203.4085   $203.41   $203.40   $203.40  
  Purchase #7 $160.97   4.276%   $167.8531   $167.85   $167.85   $167.90  
  7 purchase totals = $1,159.42       $1,253.3102   $1,253.31   $1,253.30   $1,253.40