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 $64.93   6.474%   $69.1336   $69.13   $69.15   $69.10  
  Purchase #2 $60.79   8.609%   $66.0234   $66.02   $66.00   $66.00  
  Purchase #3 $82.84   7.165%   $88.7755   $88.78   $88.80   $88.80  
  Purchase #4 $120.56   8.569%   $130.8908   $130.89   $130.90   $130.90  
  Purchase #5 $237.71   12.110%   $266.4967   $266.50   $266.50   $266.50  
  Purchase #6 $138.67   13.123%   $156.8677   $156.87   $156.85   $156.90  
  Purchase #7 $223.50   7.819%   $240.9755   $240.98   $241.00   $241.00  
  7 purchase totals = $929.00       $1,019.1632   $1,019.17   $1,019.20   $1,019.20