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 $173.49   8.165%   $187.6555   $187.66   $187.65   $187.70  
  Purchase #2 $161.79   10.640%   $179.0045   $179.00   $179.00   $179.00  
  Purchase #3 $51.61   5.406%   $54.4   $54.40   $54.40   $54.40  
  Purchase #4 $210.84   6.435%   $224.4076   $224.41   $224.40   $224.40  
  Purchase #5 $90.44   6.320%   $96.1558   $96.16   $96.15   $96.20  
  Purchase #6 $142.92   11.790%   $159.7703   $159.77   $159.75   $159.80  
  Purchase #7 $103.72   3.586%   $107.4394   $107.44   $107.45   $107.40  
  7 purchase totals = $934.81       $1,008.8331   $1,008.84   $1,008.80   $1,008.90