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 $84.83   4.424%   $88.5829   $88.58   $88.60   $88.60  
  Purchase #2 $21.61   9.453%   $23.6528   $23.65   $23.65   $23.70  
  Purchase #3 $95.71   7.654%   $103.0356   $103.04   $103.05   $103.00  
  Purchase #4 $181.27   8.384%   $196.4677   $196.47   $196.45   $196.50  
  Purchase #5 $169.54   3.471%   $175.4247   $175.42   $175.40   $175.40  
  Purchase #6 $230.41   8.350%   $249.6492   $249.65   $249.65   $249.60  
  Purchase #7 $203.82   8.578%   $221.3037   $221.30   $221.30   $221.30  
  7 purchase totals = $987.19       $1,058.1166   $1,058.11   $1,058.10   $1,058.10