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 $43.39   6.754%   $46.3206   $46.32   $46.30   $46.30  
  Purchase #2 $97.61   13.460%   $110.7483   $110.75   $110.75   $110.70  
  Purchase #3 $54.28   5.667%   $57.356   $57.36   $57.35   $57.40  
  Purchase #4 $220.79   3.632%   $228.8091   $228.81   $228.80   $228.80  
  Purchase #5 $11.60   11.385%   $12.9207   $12.92   $12.90   $12.90  
  Purchase #6 $165.90   5.490%   $175.0079   $175.01   $175.00   $175.00  
  Purchase #7 $218.33   10.648%   $241.5778   $241.58   $241.60   $241.60  
  7 purchase totals = $811.90       $872.7404   $872.75   $872.70   $872.70