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 $141.61   10.309%   $156.2086   $156.21   $156.20   $156.20  
  Purchase #2 $86.53   10.143%   $95.3067   $95.31   $95.30   $95.30  
  Purchase #3 $139.94   9.388%   $153.0776   $153.08   $153.10   $153.10  
  Purchase #4 $150.73   10.341%   $166.317   $166.32   $166.30   $166.30  
  Purchase #5 $95.96   5.502%   $101.2397   $101.24   $101.25   $101.20  
  Purchase #6 $234.62   6.831%   $250.6469   $250.65   $250.65   $250.60  
  Purchase #7 $86.53   7.289%   $92.8372   $92.84   $92.85   $92.80  
  7 purchase totals = $935.92       $1,015.6337   $1,015.65   $1,015.65   $1,015.50