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 $92.84   3.239%   $95.8471   $95.85   $95.85   $95.80  
  Purchase #2 $35.79   10.534%   $39.5601   $39.56   $39.55   $39.60  
  Purchase #3 $205.90   3.135%   $212.355   $212.36   $212.35   $212.40  
  Purchase #4 $130.77   6.506%   $139.2779   $139.28   $139.30   $139.30  
  Purchase #5 $182.48   6.736%   $194.7719   $194.77   $194.75   $194.80  
  Purchase #6 $79.82   9.319%   $87.2584   $87.26   $87.25   $87.30  
  Purchase #7 $26.92   12.668%   $30.3302   $30.33   $30.35   $30.30  
  7 purchase totals = $754.52       $799.4006   $799.41   $799.40   $799.50