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 $240.82   10.425%   $265.9255   $265.93   $265.95   $265.90  
  Purchase #2 $117.55   13.281%   $133.1618   $133.16   $133.15   $133.20  
  Purchase #3 $38.62   4.672%   $40.4243   $40.42   $40.40   $40.40  
  Purchase #4 $183.29   5.643%   $193.6331   $193.63   $193.65   $193.60  
  Purchase #5 $79.45   12.282%   $89.208   $89.21   $89.20   $89.20  
  Purchase #6 $220.85   9.486%   $241.7998   $241.80   $241.80   $241.80  
  Purchase #7 $45.42   10.869%   $50.3567   $50.36   $50.35   $50.40  
  7 purchase totals = $926.00       $1,014.5092   $1,014.51   $1,014.50   $1,014.50