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 $41.66   6.781%   $44.485   $44.49   $44.50   $44.50  
  Purchase #2 $234.26   13.820%   $266.6347   $266.63   $266.65   $266.60  
  Purchase #3 $245.25   10.746%   $271.6046   $271.60   $271.60   $271.60  
  Purchase #4 $201.82   5.803%   $213.5316   $213.53   $213.55   $213.50  
  Purchase #5 $151.31   8.280%   $163.8385   $163.84   $163.85   $163.80  
  Purchase #6 $190.45   11.711%   $212.7536   $212.75   $212.75   $212.80  
  Purchase #7 $160.62   11.241%   $178.6753   $178.68   $178.70   $178.70  
  7 purchase totals = $1,225.37       $1,351.5233   $1,351.52   $1,351.60   $1,351.50