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 $197.45   5.496%   $208.3019   $208.30   $208.30   $208.30  
  Purchase #2 $30.50   3.378%   $31.5303   $31.53   $31.55   $31.50  
  Purchase #3 $68.94   8.551%   $74.8351   $74.84   $74.85   $74.80  
  Purchase #4 $200.78   4.362%   $209.538   $209.54   $209.55   $209.50  
  Purchase #5 $144.29   11.787%   $161.2975   $161.30   $161.30   $161.30  
  Purchase #6 $86.93   10.134%   $95.7395   $95.74   $95.75   $95.70  
  Purchase #7 $202.98   9.438%   $222.1373   $222.14   $222.15   $222.10  
  7 purchase totals = $931.87       $1,003.3796   $1,003.39   $1,003.45   $1,003.20