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 $182.97   11.550%   $204.103   $204.10   $204.10   $204.10  
  Purchase #2 $61.60   5.462%   $64.9646   $64.96   $64.95   $65.00  
  Purchase #3 $238.69   13.294%   $270.4214   $270.42   $270.40   $270.40  
  Purchase #4 $113.84   11.373%   $126.787   $126.79   $126.80   $126.80  
  Purchase #5 $243.68   8.645%   $264.7461   $264.75   $264.75   $264.70  
  Purchase #6 $223.62   6.455%   $238.0547   $238.05   $238.05   $238.10  
  Purchase #7 $36.28   5.314%   $38.2079   $38.21   $38.20   $38.20  
  7 purchase totals = $1,100.68       $1,207.2847   $1,207.28   $1,207.25   $1,207.30