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 $49.82   7.442%   $53.5276   $53.53   $53.55   $53.50  
  Purchase #2 $96.96   4.470%   $101.2941   $101.29   $101.30   $101.30  
  Purchase #3 $175.48   4.206%   $182.8607   $182.86   $182.85   $182.90  
  Purchase #4 $176.91   6.367%   $188.1739   $188.17   $188.15   $188.20  
  Purchase #5 $102.64   13.572%   $116.5703   $116.57   $116.55   $116.60  
  Purchase #6 $244.47   7.640%   $263.1475   $263.15   $263.15   $263.10  
  Purchase #7 $224.58   12.205%   $251.99   $251.99   $252.00   $252.00  
  7 purchase totals = $1,070.86       $1,157.5641   $1,157.56   $1,157.55   $1,157.60