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 $177.30   11.274%   $197.2888   $197.29   $197.30   $197.30  
  Purchase #2 $173.27   7.824%   $186.8266   $186.83   $186.85   $186.80  
  Purchase #3 $69.49   5.168%   $73.0812   $73.08   $73.10   $73.10  
  Purchase #4 $184.47   4.793%   $193.3116   $193.31   $193.30   $193.30  
  Purchase #5 $87.54   4.670%   $91.6281   $91.63   $91.65   $91.60  
  Purchase #6 $200.89   4.824%   $210.5809   $210.58   $210.60   $210.60  
  Purchase #7 $181.62   3.796%   $188.5143   $188.51   $188.50   $188.50  
  7 purchase totals = $1,074.58       $1,141.2315   $1,141.23   $1,141.30   $1,141.20