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 $236.78   3.236%   $244.4422   $244.44   $244.45   $244.40  
  Purchase #2 $186.61   8.136%   $201.7926   $201.79   $201.80   $201.80  
  Purchase #3 $126.85   5.437%   $133.7468   $133.75   $133.75   $133.70  
  Purchase #4 $180.32   9.423%   $197.3116   $197.31   $197.30   $197.30  
  Purchase #5 $165.84   5.867%   $175.5698   $175.57   $175.55   $175.60  
  Purchase #6 $59.83   11.385%   $66.6416   $66.64   $66.65   $66.60  
  Purchase #7 $5.27   12.682%   $5.9383   $5.94   $5.95   $5.90  
  7 purchase totals = $961.50       $1,025.4429   $1,025.44   $1,025.45   $1,025.30