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 $214.79   9.799%   $235.8373   $235.84   $235.85   $235.80  
  Purchase #2 $149.43   11.258%   $166.2528   $166.25   $166.25   $166.30  
  Purchase #3 $20.93   13.573%   $23.7708   $23.77   $23.75   $23.80  
  Purchase #4 $210.97   12.736%   $237.8391   $237.84   $237.85   $237.80  
  Purchase #5 $227.66   9.501%   $249.29   $249.29   $249.30   $249.30  
  Purchase #6 $223.96   4.261%   $233.5029   $233.50   $233.50   $233.50  
  Purchase #7 $133.92   12.390%   $150.5127   $150.51   $150.50   $150.50  
  7 purchase totals = $1,181.66       $1,297.0056   $1,297.00   $1,297.00   $1,297.00