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 $190.45   5.811%   $201.517   $201.52   $201.50   $201.50  
  Purchase #2 $140.66   4.744%   $147.3329   $147.33   $147.35   $147.30  
  Purchase #3 $126.88   7.432%   $136.3097   $136.31   $136.30   $136.30  
  Purchase #4 $203.89   9.460%   $223.178   $223.18   $223.20   $223.20  
  Purchase #5 $119.50   4.873%   $125.3232   $125.32   $125.30   $125.30  
  Purchase #6 $118.43   4.547%   $123.815   $123.82   $123.80   $123.80  
  Purchase #7 $64.93   11.536%   $72.4203   $72.42   $72.40   $72.40  
  7 purchase totals = $964.74       $1,029.8961   $1,029.90   $1,029.85   $1,029.80