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 $183.53   12.146%   $205.8216   $205.82   $205.80   $205.80  
  Purchase #2 $233.96   4.151%   $243.6717   $243.67   $243.65   $243.70  
  Purchase #3 $190.58   10.206%   $210.0306   $210.03   $210.05   $210.00  
  Purchase #4 $84.60   6.229%   $89.8697   $89.87   $89.85   $89.90  
  Purchase #5 $224.94   7.679%   $242.2131   $242.21   $242.20   $242.20  
  Purchase #6 $32.53   12.550%   $36.6125   $36.61   $36.60   $36.60  
  Purchase #7 $26.54   12.569%   $29.8758   $29.88   $29.90   $29.90  
  7 purchase totals = $976.68       $1,058.0950   $1,058.09   $1,058.05   $1,058.10