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 $237.91   12.323%   $267.2276   $267.23   $267.25   $267.20  
  Purchase #2 $217.28   13.540%   $246.6997   $246.70   $246.70   $246.70  
  Purchase #3 $74.79   11.499%   $83.3901   $83.39   $83.40   $83.40  
  Purchase #4 $227.31   11.646%   $253.7825   $253.78   $253.80   $253.80  
  Purchase #5 $46.71   12.766%   $52.673   $52.67   $52.65   $52.70  
  Purchase #6 $50.41   10.185%   $55.5443   $55.54   $55.55   $55.50  
  Purchase #7 $225.31   5.783%   $238.3397   $238.34   $238.35   $238.30  
  7 purchase totals = $1,079.72       $1,197.6569   $1,197.65   $1,197.70   $1,197.60