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 $62.89   11.171%   $69.9154   $69.92   $69.90   $69.90  
  Purchase #2 $80.49   4.280%   $83.935   $83.94   $83.95   $83.90  
  Purchase #3 $211.56   5.610%   $223.4285   $223.43   $223.45   $223.40  
  Purchase #4 $91.87   11.558%   $102.4883   $102.49   $102.50   $102.50  
  Purchase #5 $187.47   8.256%   $202.9475   $202.95   $202.95   $202.90  
  Purchase #6 $165.80   7.250%   $177.8205   $177.82   $177.80   $177.80  
  Purchase #7 $56.96   3.113%   $58.7332   $58.73   $58.75   $58.70  
  7 purchase totals = $857.04       $919.2684   $919.28   $919.30   $919.10