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 $249.48   7.283%   $267.6496   $267.65   $267.65   $267.60  
  Purchase #2 $211.94   12.863%   $239.2018   $239.20   $239.20   $239.20  
  Purchase #3 $181.46   12.735%   $204.5689   $204.57   $204.55   $204.60  
  Purchase #4 $141.90   6.163%   $150.6453   $150.65   $150.65   $150.60  
  Purchase #5 $230.72   4.862%   $241.9376   $241.94   $241.95   $241.90  
  Purchase #6 $20.79   9.395%   $22.7432   $22.74   $22.75   $22.70  
  Purchase #7 $67.43   12.201%   $75.6571   $75.66   $75.65   $75.70  
  7 purchase totals = $1,103.72       $1,202.4035   $1,202.41   $1,202.40   $1,202.30