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 $32.97   6.494%   $35.1111   $35.11   $35.10   $35.10  
  Purchase #2 $156.46   10.592%   $173.0322   $173.03   $173.05   $173.00  
  Purchase #3 $203.73   10.190%   $224.4901   $224.49   $224.50   $224.50  
  Purchase #4 $24.64   6.120%   $26.148   $26.15   $26.15   $26.10  
  Purchase #5 $129.68   12.414%   $145.7785   $145.78   $145.80   $145.80  
  Purchase #6 $218.58   6.486%   $232.7571   $232.76   $232.75   $232.80  
  Purchase #7 $213.75   13.708%   $243.0509   $243.05   $243.05   $243.10  
  7 purchase totals = $979.81       $1,080.3679   $1,080.37   $1,080.40   $1,080.40