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 $53.87   8.821%   $58.6219   $58.62   $58.60   $58.60  
  Purchase #2 $198.33   10.731%   $219.6128   $219.61   $219.60   $219.60  
  Purchase #3 $191.54   10.279%   $211.2284   $211.23   $211.25   $211.20  
  Purchase #4 $242.40   7.317%   $260.1364   $260.14   $260.15   $260.10  
  Purchase #5 $166.99   11.768%   $186.6414   $186.64   $186.65   $186.60  
  Purchase #6 $123.87   5.767%   $131.0136   $131.01   $131.00   $131.00  
  Purchase #7 $178.79   12.607%   $201.3301   $201.33   $201.35   $201.30  
  7 purchase totals = $1,155.79       $1,268.5846   $1,268.58   $1,268.60   $1,268.40