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 $68.41   9.779%   $75.0998   $75.10   $75.10   $75.10  
  Purchase #2 $240.59   5.431%   $253.6564   $253.66   $253.65   $253.70  
  Purchase #3 $178.40   13.465%   $202.4216   $202.42   $202.40   $202.40  
  Purchase #4 $160.75   3.774%   $166.8167   $166.82   $166.80   $166.80  
  Purchase #5 $87.61   4.530%   $91.5787   $91.58   $91.60   $91.60  
  Purchase #6 $219.43   12.845%   $247.6158   $247.62   $247.60   $247.60  
  Purchase #7 $50.85   6.348%   $54.078   $54.08   $54.10   $54.10  
  7 purchase totals = $1,006.04       $1,091.2670   $1,091.28   $1,091.25   $1,091.30