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 $205.92   5.405%   $217.05   $217.05   $217.05   $217.10  
  Purchase #2 $21.33   11.662%   $23.8175   $23.82   $23.80   $23.80  
  Purchase #3 $188.38   7.411%   $202.3408   $202.34   $202.35   $202.30  
  Purchase #4 $250.51   12.575%   $282.0116   $282.01   $282.00   $282.00  
  Purchase #5 $27.86   10.245%   $30.7143   $30.71   $30.70   $30.70  
  Purchase #6 $10.92   5.293%   $11.498   $11.50   $11.50   $11.50  
  Purchase #7 $227.52   10.385%   $251.148   $251.15   $251.15   $251.10  
  7 purchase totals = $932.44       $1,018.5802   $1,018.58   $1,018.55   $1,018.50