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 $232.65   11.120%   $258.5207   $258.52   $258.50   $258.50  
  Purchase #2 $155.62   12.156%   $174.5372   $174.54   $174.55   $174.50  
  Purchase #3 $228.26   13.793%   $259.7439   $259.74   $259.75   $259.70  
  Purchase #4 $119.77   3.282%   $123.7009   $123.70   $123.70   $123.70  
  Purchase #5 $44.99   11.417%   $50.1265   $50.13   $50.15   $50.10  
  Purchase #6 $221.43   12.820%   $249.8173   $249.82   $249.80   $249.80  
  Purchase #7 $84.56   4.157%   $88.0752   $88.08   $88.10   $88.10  
  7 purchase totals = $1,087.28       $1,204.5217   $1,204.53   $1,204.55   $1,204.40