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 $241.59   13.829%   $274.9995   $275.00   $275.00   $275.00  
  Purchase #2 $243.67   11.846%   $272.5351   $272.54   $272.55   $272.50  
  Purchase #3 $188.79   9.761%   $207.2178   $207.22   $207.20   $207.20  
  Purchase #4 $245.95   8.673%   $267.2812   $267.28   $267.30   $267.30  
  Purchase #5 $41.38   10.638%   $45.782   $45.78   $45.80   $45.80  
  Purchase #6 $158.97   4.118%   $165.5164   $165.52   $165.50   $165.50  
  Purchase #7 $39.33   7.257%   $42.1842   $42.18   $42.20   $42.20  
  7 purchase totals = $1,159.68       $1,275.5162   $1,275.52   $1,275.55   $1,275.50