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 $179.53   12.283%   $201.5817   $201.58   $201.60   $201.60  
  Purchase #2 $96.95   9.538%   $106.1971   $106.20   $106.20   $106.20  
  Purchase #3 $181.91   11.813%   $203.399   $203.40   $203.40   $203.40  
  Purchase #4 $83.64   8.417%   $90.68   $90.68   $90.70   $90.70  
  Purchase #5 $137.96   13.575%   $156.6881   $156.69   $156.70   $156.70  
  Purchase #6 $65.93   9.545%   $72.223   $72.22   $72.20   $72.20  
  Purchase #7 $247.79   9.285%   $270.7973   $270.80   $270.80   $270.80  
  7 purchase totals = $993.71       $1,101.5662   $1,101.57   $1,101.60   $1,101.60