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 $219.62   3.654%   $227.6449   $227.64   $227.65   $227.60  
  Purchase #2 $196.66   4.717%   $205.9365   $205.94   $205.95   $205.90  
  Purchase #3 $184.82   3.836%   $191.9097   $191.91   $191.90   $191.90  
  Purchase #4 $93.40   8.202%   $101.0607   $101.06   $101.05   $101.10  
  Purchase #5 $108.79   11.526%   $121.3291   $121.33   $121.35   $121.30  
  Purchase #6 $6.43   11.634%   $7.1781   $7.18   $7.20   $7.20  
  Purchase #7 $93.35   13.736%   $106.1726   $106.17   $106.15   $106.20  
  7 purchase totals = $903.07       $961.2316   $961.23   $961.25   $961.20