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 $191.70   6.752%   $204.6436   $204.64   $204.65   $204.60  
  Purchase #2 $157.55   6.555%   $167.8774   $167.88   $167.90   $167.90  
  Purchase #3 $53.42   11.733%   $59.6878   $59.69   $59.70   $59.70  
  Purchase #4 $225.61   3.710%   $233.9801   $233.98   $234.00   $234.00  
  Purchase #5 $121.92   7.301%   $130.8214   $130.82   $130.80   $130.80  
  Purchase #6 $41.94   11.249%   $46.6578   $46.66   $46.65   $46.70  
  Purchase #7 $203.99   3.337%   $210.7971   $210.80   $210.80   $210.80  
  7 purchase totals = $996.13       $1,054.4652   $1,054.47   $1,054.50   $1,054.50