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 $83.31   13.472%   $94.5335   $94.53   $94.55   $94.50  
  Purchase #2 $199.80   6.403%   $212.5932   $212.59   $212.60   $212.60  
  Purchase #3 $121.46   11.309%   $135.1959   $135.20   $135.20   $135.20  
  Purchase #4 $73.27   13.275%   $82.9966   $83.00   $83.00   $83.00  
  Purchase #5 $165.88   13.632%   $188.4928   $188.49   $188.50   $188.50  
  Purchase #6 $142.88   3.456%   $147.8179   $147.82   $147.80   $147.80  
  Purchase #7 $111.39   9.498%   $121.9698   $121.97   $121.95   $122.00  
  7 purchase totals = $897.99       $983.5997   $983.60   $983.60   $983.60