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 $55.93   6.156%   $59.3731   $59.37   $59.35   $59.40  
  Purchase #2 $150.48   9.296%   $164.4686   $164.47   $164.45   $164.50  
  Purchase #3 $17.33   13.381%   $19.6489   $19.65   $19.65   $19.60  
  Purchase #4 $207.67   7.384%   $223.0044   $223.00   $223.00   $223.00  
  Purchase #5 $229.79   4.271%   $239.6043   $239.60   $239.60   $239.60  
  Purchase #6 $203.36   8.435%   $220.5134   $220.51   $220.50   $220.50  
  Purchase #7 $21.65   12.381%   $24.3305   $24.33   $24.35   $24.30  
  7 purchase totals = $886.21       $950.9432   $950.93   $950.90   $950.90