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 $223.34   10.728%   $247.2999   $247.30   $247.30   $247.30  
  Purchase #2 $110.86   13.370%   $125.682   $125.68   $125.70   $125.70  
  Purchase #3 $167.92   9.650%   $184.1243   $184.12   $184.10   $184.10  
  Purchase #4 $238.57   9.515%   $261.2699   $261.27   $261.25   $261.30  
  Purchase #5 $23.26   3.322%   $24.0327   $24.03   $24.05   $24.00  
  Purchase #6 $58.39   11.746%   $65.2485   $65.25   $65.25   $65.20  
  Purchase #7 $161.54   6.547%   $172.116   $172.12   $172.10   $172.10  
  7 purchase totals = $983.88       $1,079.7733   $1,079.77   $1,079.75   $1,079.70