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 $59.69   6.761%   $63.7256   $63.73   $63.75   $63.70  
  Purchase #2 $125.93   9.450%   $137.8304   $137.83   $137.85   $137.80  
  Purchase #3 $98.34   10.351%   $108.5192   $108.52   $108.50   $108.50  
  Purchase #4 $232.45   6.695%   $248.0125   $248.01   $248.00   $248.00  
  Purchase #5 $6.74   8.139%   $7.2886   $7.29   $7.30   $7.30  
  Purchase #6 $120.41   11.151%   $133.8369   $133.84   $133.85   $133.80  
  Purchase #7 $204.41   5.222%   $215.0843   $215.08   $215.10   $215.10  
  7 purchase totals = $847.97       $914.2975   $914.30   $914.35   $914.20