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 $159.67   11.261%   $177.6504   $177.65   $177.65   $177.70  
  Purchase #2 $195.53   8.158%   $211.4813   $211.48   $211.50   $211.50  
  Purchase #3 $184.43   6.452%   $196.3294   $196.33   $196.35   $196.30  
  Purchase #4 $61.95   7.820%   $66.7945   $66.79   $66.80   $66.80  
  Purchase #5 $165.62   9.733%   $181.7398   $181.74   $181.75   $181.70  
  Purchase #6 $110.89   13.111%   $125.4288   $125.43   $125.45   $125.40  
  Purchase #7 $151.81   12.641%   $171.0003   $171.00   $171.00   $171.00  
  7 purchase totals = $1,029.90       $1,130.4245   $1,130.42   $1,130.50   $1,130.40