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 $148.39   7.592%   $159.6558   $159.66   $159.65   $159.70  
  Purchase #2 $226.95   9.557%   $248.6396   $248.64   $248.65   $248.60  
  Purchase #3 $146.27   9.575%   $160.2754   $160.28   $160.30   $160.30  
  Purchase #4 $191.41   10.504%   $211.5157   $211.52   $211.50   $211.50  
  Purchase #5 $98.45   13.744%   $111.981   $111.98   $112.00   $112.00  
  Purchase #6 $92.61   10.406%   $102.247   $102.25   $102.25   $102.20  
  Purchase #7 $14.65   12.580%   $16.493   $16.49   $16.50   $16.50  
  7 purchase totals = $918.73       $1,010.8075   $1,010.82   $1,010.85   $1,010.80