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 $124.79   7.519%   $134.173   $134.17   $134.15   $134.20  
  Purchase #2 $120.82   12.302%   $135.6833   $135.68   $135.70   $135.70  
  Purchase #3 $170.48   5.811%   $180.3866   $180.39   $180.40   $180.40  
  Purchase #4 $227.82   6.736%   $243.166   $243.17   $243.15   $243.20  
  Purchase #5 $169.64   9.598%   $185.922   $185.92   $185.90   $185.90  
  Purchase #6 $185.54   13.507%   $210.6009   $210.60   $210.60   $210.60  
  Purchase #7 $26.85   13.648%   $30.5145   $30.51   $30.50   $30.50  
  7 purchase totals = $1,025.94       $1,120.4463   $1,120.44   $1,120.40   $1,120.50