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 $39.33   10.341%   $43.3971   $43.40   $43.40   $43.40  
  Purchase #2 $216.97   7.865%   $234.0347   $234.03   $234.05   $234.00  
  Purchase #3 $210.53   5.380%   $221.8565   $221.86   $221.85   $221.90  
  Purchase #4 $225.31   7.732%   $242.731   $242.73   $242.75   $242.70  
  Purchase #5 $211.70   12.644%   $238.4673   $238.47   $238.45   $238.50  
  Purchase #6 $151.60   13.652%   $172.2964   $172.30   $172.30   $172.30  
  Purchase #7 $88.94   7.598%   $95.6977   $95.70   $95.70   $95.70  
  7 purchase totals = $1,144.38       $1,248.4807   $1,248.49   $1,248.50   $1,248.50