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 $244.52   3.775%   $253.7506   $253.75   $253.75   $253.80  
  Purchase #2 $103.90   3.606%   $107.6466   $107.65   $107.65   $107.60  
  Purchase #3 $155.80   9.644%   $170.8254   $170.83   $170.85   $170.80  
  Purchase #4 $246.32   4.201%   $256.6679   $256.67   $256.65   $256.70  
  Purchase #5 $173.95   3.228%   $179.5651   $179.57   $179.55   $179.60  
  Purchase #6 $159.31   5.293%   $167.7423   $167.74   $167.75   $167.70  
  Purchase #7 $51.85   10.522%   $57.3057   $57.31   $57.30   $57.30  
  7 purchase totals = $1,135.65       $1,193.5036   $1,193.52   $1,193.50   $1,193.50