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 $192.27   10.141%   $211.7681   $211.77   $211.75   $211.80  
  Purchase #2 $113.55   10.607%   $125.5942   $125.59   $125.60   $125.60  
  Purchase #3 $188.82   7.308%   $202.619   $202.62   $202.60   $202.60  
  Purchase #4 $97.97   13.289%   $110.9892   $110.99   $111.00   $111.00  
  Purchase #5 $72.26   6.703%   $77.1036   $77.10   $77.10   $77.10  
  Purchase #6 $200.55   11.717%   $224.0484   $224.05   $224.05   $224.00  
  Purchase #7 $245.87   11.280%   $273.6041   $273.60   $273.60   $273.60  
  7 purchase totals = $1,111.29       $1,225.7266   $1,225.72   $1,225.70   $1,225.70