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 $85.47   9.781%   $93.8298   $93.83   $93.85   $93.80  
  Purchase #2 $25.54   4.831%   $26.7738   $26.77   $26.75   $26.80  
  Purchase #3 $123.65   5.145%   $130.0118   $130.01   $130.00   $130.00  
  Purchase #4 $154.43   13.124%   $174.6974   $174.70   $174.70   $174.70  
  Purchase #5 $143.69   5.850%   $152.0959   $152.10   $152.10   $152.10  
  Purchase #6 $187.71   9.276%   $205.122   $205.12   $205.10   $205.10  
  Purchase #7 $80.65   5.140%   $84.7954   $84.80   $84.80   $84.80  
  7 purchase totals = $801.14       $867.3261   $867.33   $867.30   $867.30