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 $235.56   13.739%   $267.9236   $267.92   $267.90   $267.90  
  Purchase #2 $197.88   9.308%   $216.2987   $216.30   $216.30   $216.30  
  Purchase #3 $134.56   4.406%   $140.4887   $140.49   $140.50   $140.50  
  Purchase #4 $204.35   8.373%   $221.4602   $221.46   $221.45   $221.50  
  Purchase #5 $99.93   9.634%   $109.5573   $109.56   $109.55   $109.60  
  Purchase #6 $44.66   4.873%   $46.8363   $46.84   $46.85   $46.80  
  Purchase #7 $64.77   13.751%   $73.6765   $73.68   $73.70   $73.70  
  7 purchase totals = $981.71       $1,076.2413   $1,076.25   $1,076.25   $1,076.30