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 $85.82   11.141%   $95.3812   $95.38   $95.40   $95.40  
  Purchase #2 $219.26   13.789%   $249.4938   $249.49   $249.50   $249.50  
  Purchase #3 $72.75   6.617%   $77.5639   $77.56   $77.55   $77.60  
  Purchase #4 $147.52   4.450%   $154.0846   $154.08   $154.10   $154.10  
  Purchase #5 $187.32   8.621%   $203.4689   $203.47   $203.45   $203.50  
  Purchase #6 $212.31   8.625%   $230.6217   $230.62   $230.60   $230.60  
  Purchase #7 $236.73   4.662%   $247.7664   $247.77   $247.75   $247.80  
  7 purchase totals = $1,161.71       $1,258.3805   $1,258.37   $1,258.35   $1,258.50