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 $33.49   12.761%   $37.7637   $37.76   $37.75   $37.80  
  Purchase #2 $197.78   6.112%   $209.8683   $209.87   $209.85   $209.90  
  Purchase #3 $176.76   8.424%   $191.6503   $191.65   $191.65   $191.70  
  Purchase #4 $116.59   13.332%   $132.1338   $132.13   $132.15   $132.10  
  Purchase #5 $47.95   5.543%   $50.6079   $50.61   $50.60   $50.60  
  Purchase #6 $213.62   3.149%   $220.3469   $220.35   $220.35   $220.30  
  Purchase #7 $161.54   6.380%   $171.8463   $171.85   $171.85   $171.80  
  7 purchase totals = $947.73       $1,014.2172   $1,014.22   $1,014.20   $1,014.20