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 $81.70   11.217%   $90.8643   $90.86   $90.85   $90.90  
  Purchase #2 $25.95   8.831%   $28.2416   $28.24   $28.25   $28.20  
  Purchase #3 $183.85   7.324%   $197.3152   $197.32   $197.30   $197.30  
  Purchase #4 $174.82   8.647%   $189.9367   $189.94   $189.95   $189.90  
  Purchase #5 $177.78   9.722%   $195.0638   $195.06   $195.05   $195.10  
  Purchase #6 $202.44   4.421%   $211.3899   $211.39   $211.40   $211.40  
  Purchase #7 $195.96   6.690%   $209.0697   $209.07   $209.05   $209.10  
  7 purchase totals = $1,042.50       $1,121.8812   $1,121.88   $1,121.85   $1,121.90