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 $186.77   8.593%   $202.8191   $202.82   $202.80   $202.80  
  Purchase #2 $230.95   4.519%   $241.3866   $241.39   $241.40   $241.40  
  Purchase #3 $182.63   6.689%   $194.8461   $194.85   $194.85   $194.80  
  Purchase #4 $54.89   12.283%   $61.6321   $61.63   $61.65   $61.60  
  Purchase #5 $128.95   5.159%   $135.6025   $135.60   $135.60   $135.60  
  Purchase #6 $200.74   4.796%   $210.3675   $210.37   $210.35   $210.40  
  Purchase #7 $67.27   12.865%   $75.9243   $75.92   $75.90   $75.90  
  7 purchase totals = $1,052.20       $1,122.5782   $1,122.58   $1,122.55   $1,122.50