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 $67.55   12.459%   $75.9661   $75.97   $75.95   $76.00  
  Purchase #2 $17.58   9.231%   $19.2028   $19.20   $19.20   $19.20  
  Purchase #3 $30.49   9.781%   $33.4722   $33.47   $33.45   $33.50  
  Purchase #4 $77.34   4.519%   $80.835   $80.84   $80.85   $80.80  
  Purchase #5 $215.30   11.458%   $239.9691   $239.97   $239.95   $240.00  
  Purchase #6 $142.91   11.844%   $159.8363   $159.84   $159.85   $159.80  
  Purchase #7 $132.58   13.704%   $150.7488   $150.75   $150.75   $150.70  
  7 purchase totals = $683.75       $760.0303   $760.04   $760.00   $760.00