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 $187.68   7.266%   $201.3168   $201.32   $201.30   $201.30  
  Purchase #2 $177.93   11.657%   $198.6713   $198.67   $198.65   $198.70  
  Purchase #3 $221.56   10.747%   $245.3711   $245.37   $245.35   $245.40  
  Purchase #4 $62.44   5.494%   $65.8705   $65.87   $65.85   $65.90  
  Purchase #5 $141.95   5.165%   $149.2817   $149.28   $149.30   $149.30  
  Purchase #6 $70.27   8.321%   $76.1172   $76.12   $76.10   $76.10  
  Purchase #7 $95.66   7.687%   $103.0134   $103.01   $103.00   $103.00  
  7 purchase totals = $957.49       $1,039.6420   $1,039.64   $1,039.55   $1,039.70