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 $191.41   5.547%   $202.0275   $202.03   $202.05   $202.00  
  Purchase #2 $25.36   4.239%   $26.435   $26.44   $26.45   $26.40  
  Purchase #3 $137.60   10.466%   $152.0012   $152.00   $152.00   $152.00  
  Purchase #4 $49.60   11.294%   $55.2018   $55.20   $55.20   $55.20  
  Purchase #5 $8.62   7.706%   $9.2843   $9.28   $9.30   $9.30  
  Purchase #6 $71.65   5.708%   $75.7398   $75.74   $75.75   $75.70  
  Purchase #7 $152.59   5.136%   $160.427   $160.43   $160.45   $160.40  
  7 purchase totals = $636.83       $681.1166   $681.12   $681.20   $681.00