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 $59.84   10.172%   $65.9269   $65.93   $65.95   $65.90  
  Purchase #2 $237.68   5.233%   $250.1178   $250.12   $250.10   $250.10  
  Purchase #3 $27.45   9.187%   $29.9718   $29.97   $29.95   $30.00  
  Purchase #4 $142.73   9.270%   $155.9611   $155.96   $155.95   $156.00  
  Purchase #5 $80.87   4.239%   $84.2981   $84.30   $84.30   $84.30  
  Purchase #6 $52.54   10.740%   $58.1828   $58.18   $58.20   $58.20  
  Purchase #7 $100.27   6.549%   $106.8367   $106.84   $106.85   $106.80  
  7 purchase totals = $701.38       $751.2952   $751.30   $751.30   $751.30