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 $63.34   12.203%   $71.0694   $71.07   $71.05   $71.10  
  Purchase #2 $247.31   6.634%   $263.7165   $263.72   $263.70   $263.70  
  Purchase #3 $58.96   9.546%   $64.5883   $64.59   $64.60   $64.60  
  Purchase #4 $111.48   3.289%   $115.1466   $115.15   $115.15   $115.10  
  Purchase #5 $177.51   3.836%   $184.3193   $184.32   $184.30   $184.30  
  Purchase #6 $23.60   6.297%   $25.0861   $25.09   $25.10   $25.10  
  Purchase #7 $243.34   12.599%   $273.9984   $274.00   $274.00   $274.00  
  7 purchase totals = $925.54       $997.9246   $997.94   $997.90   $997.90