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 $127.58   11.289%   $141.9825   $141.98   $142.00   $142.00  
  Purchase #2 $170.87   9.629%   $187.3231   $187.32   $187.30   $187.30  
  Purchase #3 $238.98   6.827%   $255.2952   $255.30   $255.30   $255.30  
  Purchase #4 $58.66   6.530%   $62.4905   $62.49   $62.50   $62.50  
  Purchase #5 $109.57   8.595%   $118.9875   $118.99   $119.00   $119.00  
  Purchase #6 $204.40   9.332%   $223.4746   $223.47   $223.45   $223.50  
  Purchase #7 $34.41   6.769%   $36.7392   $36.74   $36.75   $36.70  
  7 purchase totals = $944.47       $1,026.2926   $1,026.29   $1,026.30   $1,026.30