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 $58.28   11.261%   $64.8429   $64.84   $64.85   $64.80  
  Purchase #2 $247.99   4.124%   $258.2171   $258.22   $258.20   $258.20  
  Purchase #3 $110.61   4.655%   $115.7589   $115.76   $115.75   $115.80  
  Purchase #4 $92.36   7.410%   $99.2039   $99.20   $99.20   $99.20  
  Purchase #5 $114.35   4.585%   $119.5929   $119.59   $119.60   $119.60  
  Purchase #6 $194.40   3.565%   $201.3304   $201.33   $201.35   $201.30  
  Purchase #7 $176.52   12.547%   $198.668   $198.67   $198.65   $198.70  
  7 purchase totals = $994.51       $1,057.6141   $1,057.61   $1,057.60   $1,057.60