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 $203.95   11.547%   $227.5001   $227.50   $227.50   $227.50  
  Purchase #2 $221.33   8.241%   $239.5698   $239.57   $239.55   $239.60  
  Purchase #3 $28.52   9.753%   $31.3016   $31.30   $31.30   $31.30  
  Purchase #4 $245.55   3.118%   $253.2062   $253.21   $253.20   $253.20  
  Purchase #5 $206.54   13.349%   $234.111   $234.11   $234.10   $234.10  
  Purchase #6 $65.38   8.614%   $71.0118   $71.01   $71.00   $71.00  
  Purchase #7 $124.91   9.356%   $136.5966   $136.60   $136.60   $136.60  
  7 purchase totals = $1,096.18       $1,193.2971   $1,193.30   $1,193.25   $1,193.30