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 $53.73   12.822%   $60.6193   $60.62   $60.60   $60.60  
  Purchase #2 $184.34   10.127%   $203.0081   $203.01   $203.00   $203.00  
  Purchase #3 $26.47   5.342%   $27.884   $27.88   $27.90   $27.90  
  Purchase #4 $152.35   4.434%   $159.1052   $159.11   $159.10   $159.10  
  Purchase #5 $171.41   10.645%   $189.6566   $189.66   $189.65   $189.70  
  Purchase #6 $79.62   7.214%   $85.3638   $85.36   $85.35   $85.40  
  Purchase #7 $131.37   13.864%   $149.5831   $149.58   $149.60   $149.60  
  7 purchase totals = $799.29       $875.2201   $875.22   $875.20   $875.30