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 $86.78   11.469%   $96.7328   $96.73   $96.75   $96.70  
  Purchase #2 $52.73   6.294%   $56.0488   $56.05   $56.05   $56.00  
  Purchase #3 $200.29   5.120%   $210.5448   $210.54   $210.55   $210.50  
  Purchase #4 $144.82   5.755%   $153.1544   $153.15   $153.15   $153.20  
  Purchase #5 $132.54   12.514%   $149.1261   $149.13   $149.15   $149.10  
  Purchase #6 $121.76   12.316%   $136.756   $136.76   $136.75   $136.80  
  Purchase #7 $225.33   7.183%   $241.5155   $241.52   $241.50   $241.50  
  7 purchase totals = $964.25       $1,043.8784   $1,043.88   $1,043.90   $1,043.80