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 $53.44   6.223%   $56.7656   $56.77   $56.75   $56.80  
  Purchase #2 $123.66   5.194%   $130.0829   $130.08   $130.10   $130.10  
  Purchase #3 $220.64   13.121%   $249.5902   $249.59   $249.60   $249.60  
  Purchase #4 $186.98   7.570%   $201.1344   $201.13   $201.15   $201.10  
  Purchase #5 $203.90   9.204%   $222.667   $222.67   $222.65   $222.70  
  Purchase #6 $249.43   9.694%   $273.6097   $273.61   $273.60   $273.60  
  Purchase #7 $229.94   7.269%   $246.6543   $246.65   $246.65   $246.70  
  7 purchase totals = $1,267.99       $1,380.5041   $1,380.50   $1,380.50   $1,380.60