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 $61.77   12.672%   $69.5975   $69.60   $69.60   $69.60  
  Purchase #2 $145.95   4.838%   $153.0111   $153.01   $153.00   $153.00  
  Purchase #3 $223.40   13.515%   $253.5925   $253.59   $253.60   $253.60  
  Purchase #4 $19.40   3.753%   $20.1281   $20.13   $20.15   $20.10  
  Purchase #5 $204.28   10.708%   $226.1543   $226.15   $226.15   $226.20  
  Purchase #6 $198.57   5.449%   $209.3901   $209.39   $209.40   $209.40  
  Purchase #7 $240.94   6.254%   $256.0084   $256.01   $256.00   $256.00  
  7 purchase totals = $1,094.31       $1,187.8820   $1,187.88   $1,187.90   $1,187.90