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 $56.39   13.112%   $63.7839   $63.78   $63.80   $63.80  
  Purchase #2 $244.67   13.227%   $277.0325   $277.03   $277.05   $277.00  
  Purchase #3 $22.85   7.462%   $24.5551   $24.56   $24.55   $24.60  
  Purchase #4 $246.53   5.184%   $259.3101   $259.31   $259.30   $259.30  
  Purchase #5 $206.73   11.257%   $230.0016   $230.00   $230.00   $230.00  
  Purchase #6 $165.45   9.480%   $181.1347   $181.13   $181.15   $181.10  
  Purchase #7 $153.90   8.536%   $167.0369   $167.04   $167.05   $167.00  
  7 purchase totals = $1,096.52       $1,202.8548   $1,202.85   $1,202.90   $1,202.80