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 $70.25   13.146%   $79.4851   $79.49   $79.50   $79.50  
  Purchase #2 $183.31   5.652%   $193.6707   $193.67   $193.65   $193.70  
  Purchase #3 $59.71   7.689%   $64.3011   $64.30   $64.30   $64.30  
  Purchase #4 $138.97   7.367%   $149.2079   $149.21   $149.20   $149.20  
  Purchase #5 $231.97   8.453%   $251.5784   $251.58   $251.60   $251.60  
  Purchase #6 $120.30   8.251%   $130.226   $130.23   $130.25   $130.20  
  Purchase #7 $152.68   7.244%   $163.7401   $163.74   $163.75   $163.70  
  7 purchase totals = $957.19       $1,032.2093   $1,032.22   $1,032.25   $1,032.20