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 $187.65   8.152%   $202.9472   $202.95   $202.95   $202.90  
  Purchase #2 $225.62   11.254%   $251.0113   $251.01   $251.00   $251.00  
  Purchase #3 $243.93   13.758%   $277.4899   $277.49   $277.50   $277.50  
  Purchase #4 $69.80   13.396%   $79.1504   $79.15   $79.15   $79.20  
  Purchase #5 $10.44   4.406%   $10.9   $10.90   $10.90   $10.90  
  Purchase #6 $183.52   6.147%   $194.801   $194.80   $194.80   $194.80  
  Purchase #7 $170.51   11.224%   $189.648   $189.65   $189.65   $189.60  
  7 purchase totals = $1,091.47       $1,205.9478   $1,205.95   $1,205.95   $1,205.90