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 $55.81   11.435%   $62.1919   $62.19   $62.20   $62.20  
  Purchase #2 $224.77   13.376%   $254.8352   $254.84   $254.85   $254.80  
  Purchase #3 $118.51   5.571%   $125.1122   $125.11   $125.10   $125.10  
  Purchase #4 $187.56   12.725%   $211.427   $211.43   $211.45   $211.40  
  Purchase #5 $153.25   13.571%   $174.0476   $174.05   $174.05   $174.00  
  Purchase #6 $120.87   6.280%   $128.4606   $128.46   $128.45   $128.50  
  Purchase #7 $85.32   9.214%   $93.1814   $93.18   $93.20   $93.20  
  7 purchase totals = $946.09       $1,049.2559   $1,049.26   $1,049.30   $1,049.20