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 $174.69   12.478%   $196.4878   $196.49   $196.50   $196.50  
  Purchase #2 $190.56   7.228%   $204.3337   $204.33   $204.35   $204.30  
  Purchase #3 $228.66   6.605%   $243.763   $243.76   $243.75   $243.80  
  Purchase #4 $192.61   6.345%   $204.8311   $204.83   $204.85   $204.80  
  Purchase #5 $96.62   6.330%   $102.736   $102.74   $102.75   $102.70  
  Purchase #6 $39.51   10.862%   $43.8016   $43.80   $43.80   $43.80  
  Purchase #7 $247.59   9.140%   $270.2197   $270.22   $270.20   $270.20  
  7 purchase totals = $1,170.24       $1,266.1729   $1,266.17   $1,266.20   $1,266.10