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 $228.65   10.205%   $251.9837   $251.98   $252.00   $252.00  
  Purchase #2 $22.64   12.745%   $25.5255   $25.53   $25.55   $25.50  
  Purchase #3 $150.67   12.755%   $169.888   $169.89   $169.90   $169.90  
  Purchase #4 $82.49   4.532%   $86.2284   $86.23   $86.25   $86.20  
  Purchase #5 $88.68   9.269%   $96.8997   $96.90   $96.90   $96.90  
  Purchase #6 $14.34   4.355%   $14.9645   $14.96   $14.95   $15.00  
  Purchase #7 $245.54   10.285%   $270.7938   $270.79   $270.80   $270.80  
  7 purchase totals = $833.01       $916.2836   $916.28   $916.35   $916.30