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 $232.84   12.800%   $262.6435   $262.64   $262.65   $262.60  
  Purchase #2 $154.30   11.835%   $172.5614   $172.56   $172.55   $172.60  
  Purchase #3 $84.34   4.322%   $87.9852   $87.99   $88.00   $88.00  
  Purchase #4 $247.77   8.505%   $268.8428   $268.84   $268.85   $268.80  
  Purchase #5 $166.79   11.251%   $185.5555   $185.56   $185.55   $185.60  
  Purchase #6 $151.36   7.472%   $162.6696   $162.67   $162.65   $162.70  
  Purchase #7 $189.36   4.344%   $197.5858   $197.59   $197.60   $197.60  
  7 purchase totals = $1,226.76       $1,337.8438   $1,337.85   $1,337.85   $1,337.90