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 $85.31   4.127%   $88.8307   $88.83   $88.85   $88.80  
  Purchase #2 $240.42   13.409%   $272.6579   $272.66   $272.65   $272.70  
  Purchase #3 $52.60   4.673%   $55.058   $55.06   $55.05   $55.10  
  Purchase #4 $102.45   5.141%   $107.717   $107.72   $107.70   $107.70  
  Purchase #5 $184.58   12.615%   $207.8648   $207.86   $207.85   $207.90  
  Purchase #6 $185.64   8.169%   $200.8049   $200.80   $200.80   $200.80  
  Purchase #7 $58.64   6.449%   $62.4217   $62.42   $62.40   $62.40  
  7 purchase totals = $909.64       $995.3550   $995.35   $995.30   $995.40