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 $247.57   8.278%   $268.0638   $268.06   $268.05   $268.10  
  Purchase #2 $219.84   9.654%   $241.0634   $241.06   $241.05   $241.10  
  Purchase #3 $169.50   7.197%   $181.6989   $181.70   $181.70   $181.70  
  Purchase #4 $167.82   3.774%   $174.1535   $174.15   $174.15   $174.20  
  Purchase #5 $188.39   4.653%   $197.1558   $197.16   $197.15   $197.20  
  Purchase #6 $157.82   11.539%   $176.0308   $176.03   $176.05   $176.00  
  Purchase #7 $190.68   13.537%   $216.4924   $216.49   $216.50   $216.50  
  7 purchase totals = $1,341.62       $1,454.6586   $1,454.65   $1,454.65   $1,454.80