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 $208.33   13.569%   $236.5983   $236.60   $236.60   $236.60  
  Purchase #2 $180.36   4.865%   $189.1345   $189.13   $189.15   $189.10  
  Purchase #3 $24.82   8.516%   $26.9337   $26.93   $26.95   $26.90  
  Purchase #4 $152.39   8.855%   $165.8841   $165.88   $165.90   $165.90  
  Purchase #5 $241.84   9.386%   $264.5391   $264.54   $264.55   $264.50  
  Purchase #6 $22.52   10.471%   $24.8781   $24.88   $24.90   $24.90  
  Purchase #7 $131.79   10.829%   $146.0615   $146.06   $146.05   $146.10  
  7 purchase totals = $962.05       $1,054.0293   $1,054.02   $1,054.10   $1,054.00