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 $19.75   5.234%   $20.7837   $20.78   $20.80   $20.80  
  Purchase #2 $240.81   7.710%   $259.3765   $259.38   $259.40   $259.40  
  Purchase #3 $169.79   4.341%   $177.1606   $177.16   $177.15   $177.20  
  Purchase #4 $147.30   5.184%   $154.936   $154.94   $154.95   $154.90  
  Purchase #5 $35.37   12.386%   $39.7509   $39.75   $39.75   $39.80  
  Purchase #6 $191.29   11.181%   $212.6781   $212.68   $212.70   $212.70  
  Purchase #7 $232.57   3.363%   $240.3913   $240.39   $240.40   $240.40  
  7 purchase totals = $1,036.88       $1,105.0771   $1,105.08   $1,105.15   $1,105.20