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 $201.62   5.496%   $212.701   $212.70   $212.70   $212.70  
  Purchase #2 $59.37   5.233%   $62.4768   $62.48   $62.50   $62.50  
  Purchase #3 $29.72   7.701%   $32.0087   $32.01   $32.00   $32.00  
  Purchase #4 $209.40   11.678%   $233.8537   $233.85   $233.85   $233.90  
  Purchase #5 $134.49   9.514%   $147.2854   $147.29   $147.30   $147.30  
  Purchase #6 $201.75   7.528%   $216.9377   $216.94   $216.95   $216.90  
  Purchase #7 $162.66   5.656%   $171.86   $171.86   $171.85   $171.90  
  7 purchase totals = $999.01       $1,077.1233   $1,077.13   $1,077.15   $1,077.20