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 $29.82   9.394%   $32.6213   $32.62   $32.60   $32.60  
  Purchase #2 $125.84   8.713%   $136.8044   $136.80   $136.80   $136.80  
  Purchase #3 $194.96   12.622%   $219.5679   $219.57   $219.55   $219.60  
  Purchase #4 $121.59   4.817%   $127.447   $127.45   $127.45   $127.40  
  Purchase #5 $158.52   8.589%   $172.1353   $172.14   $172.15   $172.10  
  Purchase #6 $182.28   5.698%   $192.6663   $192.67   $192.65   $192.70  
  Purchase #7 $212.87   3.314%   $219.9245   $219.92   $219.90   $219.90  
  7 purchase totals = $1,025.88       $1,101.1667   $1,101.17   $1,101.10   $1,101.10