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 $186.76   9.211%   $203.9625   $203.96   $203.95   $204.00  
  Purchase #2 $218.26   12.350%   $245.2151   $245.22   $245.20   $245.20  
  Purchase #3 $234.54   12.714%   $264.3594   $264.36   $264.35   $264.40  
  Purchase #4 $212.55   3.769%   $220.561   $220.56   $220.55   $220.60  
  Purchase #5 $24.88   9.739%   $27.3031   $27.30   $27.30   $27.30  
  Purchase #6 $206.84   6.473%   $220.2288   $220.23   $220.25   $220.20  
  Purchase #7 $143.52   4.226%   $149.5852   $149.59   $149.60   $149.60  
  7 purchase totals = $1,227.35       $1,331.2151   $1,331.22   $1,331.20   $1,331.30