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 $187.25   13.519%   $212.5643   $212.56   $212.55   $212.60  
  Purchase #2 $99.47   5.773%   $105.2124   $105.21   $105.20   $105.20  
  Purchase #3 $221.73   5.241%   $233.3509   $233.35   $233.35   $233.40  
  Purchase #4 $23.74   5.348%   $25.0096   $25.01   $25.00   $25.00  
  Purchase #5 $89.63   3.708%   $92.9535   $92.95   $92.95   $93.00  
  Purchase #6 $102.98   3.215%   $106.2908   $106.29   $106.30   $106.30  
  Purchase #7 $247.29   13.754%   $281.3023   $281.30   $281.30   $281.30  
  7 purchase totals = $972.09       $1,056.6838   $1,056.67   $1,056.65   $1,056.80