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 $246.35   3.115%   $254.0238   $254.02   $254.00   $254.00  
  Purchase #2 $228.29   6.270%   $242.6038   $242.60   $242.60   $242.60  
  Purchase #3 $56.57   6.199%   $60.0768   $60.08   $60.10   $60.10  
  Purchase #4 $37.31   4.412%   $38.9561   $38.96   $38.95   $39.00  
  Purchase #5 $58.98   8.114%   $63.7656   $63.77   $63.75   $63.80  
  Purchase #6 $230.41   4.130%   $239.9259   $239.93   $239.95   $239.90  
  Purchase #7 $110.62   12.670%   $124.6356   $124.64   $124.65   $124.60  
  7 purchase totals = $968.53       $1,023.9876   $1,024.00   $1,024.00   $1,024.00