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 $116.39   8.524%   $126.3111   $126.31   $126.30   $126.30  
  Purchase #2 $126.53   8.856%   $137.7355   $137.74   $137.75   $137.70  
  Purchase #3 $165.64   13.181%   $187.473   $187.47   $187.45   $187.50  
  Purchase #4 $143.52   12.782%   $161.8647   $161.86   $161.85   $161.90  
  Purchase #5 $141.55   13.666%   $160.8942   $160.89   $160.90   $160.90  
  Purchase #6 $216.49   8.303%   $234.4652   $234.47   $234.45   $234.50  
  Purchase #7 $34.86   11.168%   $38.7532   $38.75   $38.75   $38.80  
  7 purchase totals = $944.98       $1,047.4969   $1,047.49   $1,047.45   $1,047.60