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 $235.58   12.623%   $265.3173   $265.32   $265.30   $265.30  
  Purchase #2 $44.97   12.526%   $50.6029   $50.60   $50.60   $50.60  
  Purchase #3 $243.87   13.835%   $277.6094   $277.61   $277.60   $277.60  
  Purchase #4 $99.78   10.755%   $110.5113   $110.51   $110.50   $110.50  
  Purchase #5 $72.52   5.554%   $76.5478   $76.55   $76.55   $76.50  
  Purchase #6 $5.84   4.497%   $6.1026   $6.10   $6.10   $6.10  
  Purchase #7 $246.31   13.323%   $279.1259   $279.13   $279.15   $279.10  
  7 purchase totals = $948.87       $1,065.8172   $1,065.82   $1,065.80   $1,065.70