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 $123.86   8.198%   $134.014   $134.01   $134.00   $134.00  
  Purchase #2 $203.53   12.613%   $229.2012   $229.20   $229.20   $229.20  
  Purchase #3 $186.75   11.210%   $207.6847   $207.68   $207.70   $207.70  
  Purchase #4 $111.44   4.797%   $116.7858   $116.79   $116.80   $116.80  
  Purchase #5 $176.27   8.629%   $191.4803   $191.48   $191.50   $191.50  
  Purchase #6 $215.57   8.110%   $233.0527   $233.05   $233.05   $233.10  
  Purchase #7 $156.87   10.506%   $173.3508   $173.35   $173.35   $173.40  
  7 purchase totals = $1,174.29       $1,285.5695   $1,285.56   $1,285.60   $1,285.70