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 $87.83   9.830%   $96.4637   $96.46   $96.45   $96.50  
  Purchase #2 $33.62   7.631%   $36.1855   $36.19   $36.20   $36.20  
  Purchase #3 $211.25   13.838%   $240.4828   $240.48   $240.50   $240.50  
  Purchase #4 $174.86   3.510%   $180.9976   $181.00   $181.00   $181.00  
  Purchase #5 $79.51   5.227%   $83.666   $83.67   $83.65   $83.70  
  Purchase #6 $180.48   12.115%   $202.3452   $202.35   $202.35   $202.30  
  Purchase #7 $22.44   10.453%   $24.7857   $24.79   $24.80   $24.80  
  7 purchase totals = $789.99       $864.9265   $864.94   $864.95   $865.00