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 $244.85   3.232%   $252.7636   $252.76   $252.75   $252.80  
  Purchase #2 $183.61   11.165%   $204.1101   $204.11   $204.10   $204.10  
  Purchase #3 $20.85   8.559%   $22.6346   $22.63   $22.65   $22.60  
  Purchase #4 $152.52   12.437%   $171.4889   $171.49   $171.50   $171.50  
  Purchase #5 $220.31   6.593%   $234.835   $234.84   $234.85   $234.80  
  Purchase #6 $218.44   11.292%   $243.1062   $243.11   $243.10   $243.10  
  Purchase #7 $154.46   12.689%   $174.0594   $174.06   $174.05   $174.10  
  7 purchase totals = $1,195.04       $1,302.9978   $1,303.00   $1,303.00   $1,303.00