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 $210.66   9.542%   $230.7612   $230.76   $230.75   $230.80  
  Purchase #2 $59.84   3.622%   $62.0074   $62.01   $62.00   $62.00  
  Purchase #3 $34.84   9.146%   $38.0265   $38.03   $38.05   $38.00  
  Purchase #4 $82.33   12.496%   $92.618   $92.62   $92.60   $92.60  
  Purchase #5 $87.34   13.682%   $99.2899   $99.29   $99.30   $99.30  
  Purchase #6 $243.85   8.274%   $264.0261   $264.03   $264.05   $264.00  
  Purchase #7 $11.29   9.393%   $12.3505   $12.35   $12.35   $12.40  
  7 purchase totals = $730.15       $799.0796   $799.09   $799.10   $799.10