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 $223.53   5.279%   $235.3301   $235.33   $235.35   $235.30  
  Purchase #2 $226.95   10.415%   $250.5868   $250.59   $250.60   $250.60  
  Purchase #3 $31.34   3.873%   $32.5538   $32.55   $32.55   $32.60  
  Purchase #4 $207.84   7.665%   $223.7709   $223.77   $223.75   $223.80  
  Purchase #5 $121.67   13.378%   $137.947   $137.95   $137.95   $137.90  
  Purchase #6 $189.49   7.678%   $204.039   $204.04   $204.05   $204.00  
  Purchase #7 $176.63   4.339%   $184.294   $184.29   $184.30   $184.30  
  7 purchase totals = $1,177.45       $1,268.5216   $1,268.52   $1,268.55   $1,268.50