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 $87.80   6.308%   $93.3384   $93.34   $93.35   $93.30  
  Purchase #2 $236.67   12.636%   $266.5756   $266.58   $266.60   $266.60  
  Purchase #3 $179.76   3.833%   $186.6502   $186.65   $186.65   $186.70  
  Purchase #4 $126.98   5.862%   $134.4236   $134.42   $134.40   $134.40  
  Purchase #5 $111.48   12.282%   $125.172   $125.17   $125.15   $125.20  
  Purchase #6 $184.96   4.772%   $193.7863   $193.79   $193.80   $193.80  
  Purchase #7 $203.88   6.356%   $216.8386   $216.84   $216.85   $216.80  
  7 purchase totals = $1,131.53       $1,216.7847   $1,216.79   $1,216.80   $1,216.80