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 $62.97   8.131%   $68.0901   $68.09   $68.10   $68.10  
  Purchase #2 $207.41   9.314%   $226.7282   $226.73   $226.75   $226.70  
  Purchase #3 $129.52   11.408%   $144.2956   $144.30   $144.30   $144.30  
  Purchase #4 $5.57   7.715%   $5.9997   $6.00   $6.00   $6.00  
  Purchase #5 $195.47   13.585%   $222.0246   $222.02   $222.00   $222.00  
  Purchase #6 $172.85   12.242%   $194.0103   $194.01   $194.00   $194.00  
  Purchase #7 $124.58   7.263%   $133.6282   $133.63   $133.65   $133.60  
  7 purchase totals = $898.37       $994.7767   $994.78   $994.80   $994.70