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 $86.87   6.698%   $92.6886   $92.69   $92.70   $92.70  
  Purchase #2 $72.76   6.568%   $77.5389   $77.54   $77.55   $77.50  
  Purchase #3 $115.85   4.666%   $121.2556   $121.26   $121.25   $121.30  
  Purchase #4 $199.89   12.779%   $225.4339   $225.43   $225.45   $225.40  
  Purchase #5 $239.30   11.424%   $266.6376   $266.64   $266.65   $266.60  
  Purchase #6 $204.56   3.290%   $211.29   $211.29   $211.30   $211.30  
  Purchase #7 $167.72   7.539%   $180.3644   $180.36   $180.35   $180.40  
  7 purchase totals = $1,086.95       $1,175.2090   $1,175.21   $1,175.25   $1,175.20