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 $66.50   4.806%   $69.696   $69.70   $69.70   $69.70  
  Purchase #2 $153.84   7.598%   $165.5288   $165.53   $165.55   $165.50  
  Purchase #3 $245.94   5.821%   $260.2562   $260.26   $260.25   $260.30  
  Purchase #4 $205.26   13.705%   $233.3909   $233.39   $233.40   $233.40  
  Purchase #5 $134.91   7.507%   $145.0377   $145.04   $145.05   $145.00  
  Purchase #6 $47.50   12.126%   $53.2599   $53.26   $53.25   $53.30  
  Purchase #7 $96.78   6.272%   $102.85   $102.85   $102.85   $102.90  
  7 purchase totals = $950.73       $1,030.0195   $1,030.03   $1,030.05   $1,030.10