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 $52.83   7.595%   $56.8424   $56.84   $56.85   $56.80  
  Purchase #2 $50.48   9.371%   $55.2105   $55.21   $55.20   $55.20  
  Purchase #3 $229.62   10.152%   $252.931   $252.93   $252.95   $252.90  
  Purchase #4 $120.28   10.254%   $132.6135   $132.61   $132.60   $132.60  
  Purchase #5 $104.37   11.167%   $116.025   $116.03   $116.05   $116.00  
  Purchase #6 $226.26   5.616%   $238.9668   $238.97   $238.95   $239.00  
  Purchase #7 $161.42   11.467%   $179.93   $179.93   $179.95   $179.90  
  7 purchase totals = $945.26       $1,032.5192   $1,032.52   $1,032.55   $1,032.40