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 $204.25   5.621%   $215.7309   $215.73   $215.75   $215.70  
  Purchase #2 $243.97   12.251%   $273.8588   $273.86   $273.85   $273.90  
  Purchase #3 $118.90   12.294%   $133.5176   $133.52   $133.50   $133.50  
  Purchase #4 $88.55   6.816%   $94.5856   $94.59   $94.60   $94.60  
  Purchase #5 $149.73   4.245%   $156.086   $156.09   $156.10   $156.10  
  Purchase #6 $163.42   9.286%   $178.5952   $178.60   $178.60   $178.60  
  Purchase #7 $194.64   4.789%   $203.9613   $203.96   $203.95   $204.00  
  7 purchase totals = $1,163.46       $1,256.3354   $1,256.35   $1,256.35   $1,256.40