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 $243.79   13.417%   $276.4993   $276.50   $276.50   $276.50  
  Purchase #2 $49.81   7.414%   $53.5029   $53.50   $53.50   $53.50  
  Purchase #3 $190.65   7.351%   $204.6647   $204.66   $204.65   $204.70  
  Purchase #4 $174.68   11.154%   $194.1638   $194.16   $194.15   $194.20  
  Purchase #5 $176.59   10.716%   $195.5134   $195.51   $195.50   $195.50  
  Purchase #6 $194.60   12.521%   $218.9659   $218.97   $218.95   $219.00  
  Purchase #7 $173.49   4.648%   $181.5538   $181.55   $181.55   $181.60  
  7 purchase totals = $1,203.61       $1,324.8638   $1,324.85   $1,324.80   $1,325.00