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 $53.34   5.771%   $56.4183   $56.42   $56.40   $56.40  
  Purchase #2 $160.96   12.472%   $181.0349   $181.03   $181.05   $181.00  
  Purchase #3 $219.45   12.539%   $246.9668   $246.97   $246.95   $247.00  
  Purchase #4 $140.26   12.598%   $157.93   $157.93   $157.95   $157.90  
  Purchase #5 $116.98   4.565%   $122.3201   $122.32   $122.30   $122.30  
  Purchase #6 $77.28   3.594%   $80.0574   $80.06   $80.05   $80.10  
  Purchase #7 $191.44   12.827%   $215.996   $216.00   $216.00   $216.00  
  7 purchase totals = $959.71       $1,060.7235   $1,060.73   $1,060.70   $1,060.70