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 $244.95   5.859%   $259.3016   $259.30   $259.30   $259.30  
  Purchase #2 $243.51   13.761%   $277.0194   $277.02   $277.00   $277.00  
  Purchase #3 $50.31   6.826%   $53.7442   $53.74   $53.75   $53.70  
  Purchase #4 $189.47   7.220%   $203.1497   $203.15   $203.15   $203.10  
  Purchase #5 $167.89   4.820%   $175.9823   $175.98   $176.00   $176.00  
  Purchase #6 $52.71   6.586%   $56.1815   $56.18   $56.20   $56.20  
  Purchase #7 $153.50   6.322%   $163.2043   $163.20   $163.20   $163.20  
  7 purchase totals = $1,102.34       $1,188.5830   $1,188.57   $1,188.60   $1,188.50