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 $61.84   5.172%   $65.0384   $65.04   $65.05   $65.00  
  Purchase #2 $154.64   11.399%   $172.2674   $172.27   $172.25   $172.30  
  Purchase #3 $195.79   8.619%   $212.6651   $212.67   $212.65   $212.70  
  Purchase #4 $80.25   7.120%   $85.9638   $85.96   $85.95   $86.00  
  Purchase #5 $147.50   6.867%   $157.6288   $157.63   $157.65   $157.60  
  Purchase #6 $93.97   13.847%   $106.982   $106.98   $107.00   $107.00  
  Purchase #7 $247.89   13.185%   $280.5743   $280.57   $280.55   $280.60  
  7 purchase totals = $981.88       $1,081.1198   $1,081.12   $1,081.10   $1,081.20