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 $34.43   6.464%   $36.6556   $36.66   $36.65   $36.70  
  Purchase #2 $180.32   13.604%   $204.8507   $204.85   $204.85   $204.90  
  Purchase #3 $219.51   6.511%   $233.8023   $233.80   $233.80   $233.80  
  Purchase #4 $201.76   11.169%   $224.2946   $224.29   $224.30   $224.30  
  Purchase #5 $69.51   5.628%   $73.422   $73.42   $73.40   $73.40  
  Purchase #6 $119.36   7.362%   $128.1473   $128.15   $128.15   $128.10  
  Purchase #7 $133.84   12.102%   $150.0373   $150.04   $150.05   $150.00  
  7 purchase totals = $958.73       $1,051.2098   $1,051.21   $1,051.20   $1,051.20