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 $234.56   8.307%   $254.0449   $254.04   $254.05   $254.00  
  Purchase #2 $232.60   12.781%   $262.3286   $262.33   $262.35   $262.30  
  Purchase #3 $53.51   12.574%   $60.2383   $60.24   $60.25   $60.20  
  Purchase #4 $60.90   12.759%   $68.6702   $68.67   $68.65   $68.70  
  Purchase #5 $130.95   4.513%   $136.8598   $136.86   $136.85   $136.90  
  Purchase #6 $135.54   8.689%   $147.3171   $147.32   $147.30   $147.30  
  Purchase #7 $219.90   4.867%   $230.6025   $230.60   $230.60   $230.60  
  7 purchase totals = $1,067.96       $1,160.0614   $1,160.06   $1,160.05   $1,160.00