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 $194.65   6.194%   $206.7066   $206.71   $206.70   $206.70  
  Purchase #2 $180.92   11.823%   $202.3102   $202.31   $202.30   $202.30  
  Purchase #3 $8.79   12.562%   $9.8942   $9.89   $9.90   $9.90  
  Purchase #4 $40.82   13.814%   $46.4589   $46.46   $46.45   $46.50  
  Purchase #5 $71.25   5.796%   $75.3797   $75.38   $75.40   $75.40  
  Purchase #6 $246.81   3.236%   $254.7968   $254.80   $254.80   $254.80  
  Purchase #7 $139.32   4.341%   $145.3679   $145.37   $145.35   $145.40  
  7 purchase totals = $882.56       $940.9143   $940.92   $940.90   $941.00