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 $125.61   5.317%   $132.2887   $132.29   $132.30   $132.30  
  Purchase #2 $243.62   13.211%   $275.8046   $275.80   $275.80   $275.80  
  Purchase #3 $182.33   10.557%   $201.5786   $201.58   $201.60   $201.60  
  Purchase #4 $201.82   6.284%   $214.5024   $214.50   $214.50   $214.50  
  Purchase #5 $75.77   5.518%   $79.951   $79.95   $79.95   $80.00  
  Purchase #6 $129.29   4.407%   $134.9878   $134.99   $135.00   $135.00  
  Purchase #7 $192.78   11.630%   $215.2003   $215.20   $215.20   $215.20  
  7 purchase totals = $1,151.22       $1,254.3134   $1,254.31   $1,254.35   $1,254.40