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 $83.74   11.663%   $93.5066   $93.51   $93.50   $93.50  
  Purchase #2 $29.57   9.227%   $32.2984   $32.30   $32.30   $32.30  
  Purchase #3 $136.91   13.866%   $155.8939   $155.89   $155.90   $155.90  
  Purchase #4 $136.94   9.243%   $149.5974   $149.60   $149.60   $149.60  
  Purchase #5 $166.35   6.662%   $177.4322   $177.43   $177.45   $177.40  
  Purchase #6 $183.94   10.724%   $203.6657   $203.67   $203.65   $203.70  
  Purchase #7 $243.64   8.645%   $264.7027   $264.70   $264.70   $264.70  
  7 purchase totals = $981.09       $1,077.0969   $1,077.10   $1,077.10   $1,077.10