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 $68.97   7.742%   $74.3097   $74.31   $74.30   $74.30  
  Purchase #2 $227.49   11.306%   $253.21   $253.21   $253.20   $253.20  
  Purchase #3 $76.33   4.850%   $80.032   $80.03   $80.05   $80.00  
  Purchase #4 $21.88   4.107%   $22.7786   $22.78   $22.80   $22.80  
  Purchase #5 $184.78   5.345%   $194.6565   $194.66   $194.65   $194.70  
  Purchase #6 $96.77   3.587%   $100.2411   $100.24   $100.25   $100.20  
  Purchase #7 $42.40   4.568%   $44.3368   $44.34   $44.35   $44.30  
  7 purchase totals = $718.62       $769.5647   $769.57   $769.60   $769.50