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 $32.35   8.182%   $34.9969   $35.00   $35.00   $35.00  
  Purchase #2 $179.35   13.428%   $203.4331   $203.43   $203.45   $203.40  
  Purchase #3 $243.96   6.127%   $258.9074   $258.91   $258.90   $258.90  
  Purchase #4 $97.70   8.702%   $106.2019   $106.20   $106.20   $106.20  
  Purchase #5 $154.65   4.244%   $161.2133   $161.21   $161.20   $161.20  
  Purchase #6 $209.56   9.630%   $229.7406   $229.74   $229.75   $229.70  
  Purchase #7 $58.49   10.380%   $64.5613   $64.56   $64.55   $64.60  
  7 purchase totals = $976.06       $1,059.0545   $1,059.05   $1,059.05   $1,059.00