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 $76.40   3.295%   $78.9174   $78.92   $78.90   $78.90  
  Purchase #2 $120.65   8.578%   $130.9994   $131.00   $131.00   $131.00  
  Purchase #3 $62.75   5.743%   $66.3537   $66.35   $66.35   $66.40  
  Purchase #4 $217.87   6.164%   $231.2995   $231.30   $231.30   $231.30  
  Purchase #5 $124.79   9.611%   $136.7836   $136.78   $136.80   $136.80  
  Purchase #6 $153.43   4.279%   $159.9953   $160.00   $160.00   $160.00  
  Purchase #7 $202.35   8.321%   $219.1875   $219.19   $219.20   $219.20  
  7 purchase totals = $958.24       $1,023.5364   $1,023.54   $1,023.55   $1,023.60