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 $246.82   6.666%   $263.273   $263.27   $263.25   $263.30  
  Purchase #2 $214.33   12.402%   $240.9112   $240.91   $240.90   $240.90  
  Purchase #3 $28.50   4.162%   $29.6862   $29.69   $29.70   $29.70  
  Purchase #4 $211.92   9.854%   $232.8026   $232.80   $232.80   $232.80  
  Purchase #5 $49.50   6.460%   $52.6977   $52.70   $52.70   $52.70  
  Purchase #6 $232.33   9.459%   $254.3061   $254.31   $254.30   $254.30  
  Purchase #7 $220.28   7.441%   $236.671   $236.67   $236.65   $236.70  
  7 purchase totals = $1,203.68       $1,310.3478   $1,310.35   $1,310.30   $1,310.40