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 $222.81   5.802%   $235.7374   $235.74   $235.75   $235.70  
  Purchase #2 $152.98   11.619%   $170.7547   $170.75   $170.75   $170.80  
  Purchase #3 $183.75   7.485%   $197.5037   $197.50   $197.50   $197.50  
  Purchase #4 $224.52   6.238%   $238.5256   $238.53   $238.55   $238.50  
  Purchase #5 $96.29   8.334%   $104.3148   $104.31   $104.30   $104.30  
  Purchase #6 $136.95   4.822%   $143.5537   $143.55   $143.55   $143.60  
  Purchase #7 $174.79   3.295%   $180.5493   $180.55   $180.55   $180.50  
  7 purchase totals = $1,192.09       $1,270.9392   $1,270.93   $1,270.95   $1,270.90