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 $82.32   13.349%   $93.3089   $93.31   $93.30   $93.30  
  Purchase #2 $58.46   5.165%   $61.4795   $61.48   $61.50   $61.50  
  Purchase #3 $181.94   10.281%   $200.6453   $200.65   $200.65   $200.60  
  Purchase #4 $192.63   5.128%   $202.5081   $202.51   $202.50   $202.50  
  Purchase #5 $206.40   4.485%   $215.657   $215.66   $215.65   $215.70  
  Purchase #6 $176.35   13.851%   $200.7762   $200.78   $200.80   $200.80  
  Purchase #7 $211.63   11.447%   $235.8553   $235.86   $235.85   $235.90  
  7 purchase totals = $1,109.73       $1,210.2303   $1,210.25   $1,210.25   $1,210.30