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 $29.92   9.733%   $32.8321   $32.83   $32.85   $32.80  
  Purchase #2 $37.80   7.616%   $40.6788   $40.68   $40.70   $40.70  
  Purchase #3 $146.45   10.697%   $162.1158   $162.12   $162.10   $162.10  
  Purchase #4 $218.77   9.300%   $239.1156   $239.12   $239.10   $239.10  
  Purchase #5 $207.78   7.632%   $223.6378   $223.64   $223.65   $223.60  
  Purchase #6 $151.80   13.357%   $172.0759   $172.08   $172.10   $172.10  
  Purchase #7 $211.67   3.797%   $219.7071   $219.71   $219.70   $219.70  
  7 purchase totals = $1,004.19       $1,090.1631   $1,090.18   $1,090.20   $1,090.10