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 $67.76   10.749%   $75.0435   $75.04   $75.05   $75.00  
  Purchase #2 $211.48   9.479%   $231.5262   $231.53   $231.55   $231.50  
  Purchase #3 $216.77   12.276%   $243.3807   $243.38   $243.40   $243.40  
  Purchase #4 $221.53   6.695%   $236.3614   $236.36   $236.35   $236.40  
  Purchase #5 $39.64   3.544%   $41.0448   $41.04   $41.05   $41.00  
  Purchase #6 $38.38   11.514%   $42.7991   $42.80   $42.80   $42.80  
  Purchase #7 $80.98   3.385%   $83.7212   $83.72   $83.70   $83.70  
  7 purchase totals = $876.54       $953.8769   $953.87   $953.90   $953.80