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 $194.38   3.512%   $201.2066   $201.21   $201.20   $201.20  
  Purchase #2 $124.61   4.124%   $129.7489   $129.75   $129.75   $129.70  
  Purchase #3 $167.86   7.277%   $180.0752   $180.08   $180.10   $180.10  
  Purchase #4 $244.28   7.230%   $261.9414   $261.94   $261.95   $261.90  
  Purchase #5 $16.79   12.245%   $18.8459   $18.85   $18.85   $18.80  
  Purchase #6 $116.97   6.276%   $124.311   $124.31   $124.30   $124.30  
  Purchase #7 $102.72   3.472%   $106.2864   $106.29   $106.30   $106.30  
  7 purchase totals = $967.61       $1,022.4154   $1,022.43   $1,022.45   $1,022.30