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 $67.91   8.780%   $73.8725   $73.87   $73.85   $73.90  
  Purchase #2 $219.53   8.405%   $237.9815   $237.98   $238.00   $238.00  
  Purchase #3 $53.81   11.816%   $60.1682   $60.17   $60.15   $60.20  
  Purchase #4 $65.43   10.855%   $72.5324   $72.53   $72.55   $72.50  
  Purchase #5 $208.41   6.213%   $221.3585   $221.36   $221.35   $221.40  
  Purchase #6 $74.48   8.442%   $80.7676   $80.77   $80.75   $80.80  
  Purchase #7 $19.58   6.789%   $20.9093   $20.91   $20.90   $20.90  
  7 purchase totals = $709.15       $767.5900   $767.59   $767.55   $767.70