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 $157.38   6.470%   $167.5625   $167.56   $167.55   $167.60  
  Purchase #2 $24.89   3.367%   $25.728   $25.73   $25.75   $25.70  
  Purchase #3 $137.35   3.236%   $141.7946   $141.79   $141.80   $141.80  
  Purchase #4 $135.96   9.662%   $149.0965   $149.10   $149.10   $149.10  
  Purchase #5 $219.74   5.110%   $230.9687   $230.97   $230.95   $231.00  
  Purchase #6 $43.68   5.197%   $45.95   $45.95   $45.95   $46.00  
  Purchase #7 $143.41   6.112%   $152.1752   $152.18   $152.20   $152.20  
  7 purchase totals = $862.41       $913.2755   $913.28   $913.30   $913.40