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 $232.29   13.740%   $264.2066   $264.21   $264.20   $264.20  
  Purchase #2 $190.82   7.421%   $204.9808   $204.98   $205.00   $205.00  
  Purchase #3 $119.92   3.845%   $124.5309   $124.53   $124.55   $124.50  
  Purchase #4 $167.33   6.706%   $178.5511   $178.55   $178.55   $178.60  
  Purchase #5 $211.47   8.182%   $228.7725   $228.77   $228.75   $228.80  
  Purchase #6 $196.29   6.844%   $209.7241   $209.72   $209.70   $209.70  
  Purchase #7 $246.27   3.717%   $255.4239   $255.42   $255.40   $255.40  
  7 purchase totals = $1,364.39       $1,466.1899   $1,466.18   $1,466.15   $1,466.20