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 $217.50   6.677%   $232.0225   $232.02   $232.00   $232.00  
  Purchase #2 $212.78   11.738%   $237.7561   $237.76   $237.75   $237.80  
  Purchase #3 $219.46   12.631%   $247.18   $247.18   $247.20   $247.20  
  Purchase #4 $193.35   4.506%   $202.0624   $202.06   $202.05   $202.10  
  Purchase #5 $85.33   4.479%   $89.1519   $89.15   $89.15   $89.20  
  Purchase #6 $20.83   12.371%   $23.4069   $23.41   $23.40   $23.40  
  Purchase #7 $11.38   3.226%   $11.7471   $11.75   $11.75   $11.70  
  7 purchase totals = $960.63       $1,043.3269   $1,043.33   $1,043.30   $1,043.40