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 $84.71   11.203%   $94.2001   $94.20   $94.20   $94.20  
  Purchase #2 $50.43   7.146%   $54.0337   $54.03   $54.05   $54.00  
  Purchase #3 $208.31   13.465%   $236.3589   $236.36   $236.35   $236.40  
  Purchase #4 $113.73   8.456%   $123.347   $123.35   $123.35   $123.30  
  Purchase #5 $205.53   13.194%   $232.6476   $232.65   $232.65   $232.60  
  Purchase #6 $178.68   6.290%   $189.919   $189.92   $189.90   $189.90  
  Purchase #7 $142.39   3.405%   $147.2384   $147.24   $147.25   $147.20  
  7 purchase totals = $983.78       $1,077.7447   $1,077.75   $1,077.75   $1,077.60