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 $161.32   8.112%   $174.4063   $174.41   $174.40   $174.40  
  Purchase #2 $140.77   12.737%   $158.6999   $158.70   $158.70   $158.70  
  Purchase #3 $59.61   6.565%   $63.5234   $63.52   $63.50   $63.50  
  Purchase #4 $166.74   6.817%   $178.1067   $178.11   $178.10   $178.10  
  Purchase #5 $106.37   12.559%   $119.729   $119.73   $119.75   $119.70  
  Purchase #6 $85.32   9.171%   $93.1447   $93.14   $93.15   $93.10  
  Purchase #7 $216.98   9.843%   $238.3373   $238.34   $238.35   $238.30  
  7 purchase totals = $937.11       $1,025.9473   $1,025.95   $1,025.95   $1,025.80