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 $193.62   9.586%   $212.1804   $212.18   $212.20   $212.20  
  Purchase #2 $126.49   10.176%   $139.3616   $139.36   $139.35   $139.40  
  Purchase #3 $240.42   12.371%   $270.1624   $270.16   $270.15   $270.20  
  Purchase #4 $202.65   5.579%   $213.9558   $213.96   $213.95   $214.00  
  Purchase #5 $231.25   10.171%   $254.7704   $254.77   $254.75   $254.80  
  Purchase #6 $225.53   7.565%   $242.5913   $242.59   $242.60   $242.60  
  Purchase #7 $32.82   8.121%   $35.4853   $35.49   $35.50   $35.50  
  7 purchase totals = $1,252.78       $1,368.5072   $1,368.51   $1,368.50   $1,368.70