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 $175.88   12.319%   $197.5467   $197.55   $197.55   $197.50  
  Purchase #2 $112.27   9.239%   $122.6426   $122.64   $122.65   $122.60  
  Purchase #3 $223.55   4.702%   $234.0613   $234.06   $234.05   $234.10  
  Purchase #4 $22.75   8.660%   $24.7202   $24.72   $24.70   $24.70  
  Purchase #5 $8.65   5.525%   $9.1279   $9.13   $9.15   $9.10  
  Purchase #6 $181.64   12.471%   $204.2923   $204.29   $204.30   $204.30  
  Purchase #7 $137.90   7.594%   $148.3721   $148.37   $148.35   $148.40  
  7 purchase totals = $862.64       $940.7631   $940.76   $940.75   $940.70