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 $213.80   8.544%   $232.0671   $232.07   $232.05   $232.10  
  Purchase #2 $243.42   8.804%   $264.8507   $264.85   $264.85   $264.90  
  Purchase #3 $76.74   10.335%   $84.6711   $84.67   $84.65   $84.70  
  Purchase #4 $140.96   6.290%   $149.8264   $149.83   $149.85   $149.80  
  Purchase #5 $161.25   6.237%   $171.3072   $171.31   $171.30   $171.30  
  Purchase #6 $36.80   7.868%   $39.6954   $39.70   $39.70   $39.70  
  Purchase #7 $58.74   9.433%   $64.2809   $64.28   $64.30   $64.30  
  7 purchase totals = $931.71       $1,006.6988   $1,006.71   $1,006.70   $1,006.80