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 $196.79   12.822%   $222.0224   $222.02   $222.00   $222.00  
  Purchase #2 $165.63   13.432%   $187.8774   $187.88   $187.90   $187.90  
  Purchase #3 $36.55   6.769%   $39.0241   $39.02   $39.00   $39.00  
  Purchase #4 $163.35   6.400%   $173.8044   $173.80   $173.80   $173.80  
  Purchase #5 $87.97   6.829%   $93.9775   $93.98   $94.00   $94.00  
  Purchase #6 $28.39   9.229%   $31.0101   $31.01   $31.00   $31.00  
  Purchase #7 $92.73   9.637%   $101.6664   $101.67   $101.65   $101.70  
  7 purchase totals = $771.41       $849.3823   $849.38   $849.35   $849.40