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 $106.77   4.273%   $111.3323   $111.33   $111.35   $111.30  
  Purchase #2 $10.73   5.626%   $11.3337   $11.33   $11.35   $11.30  
  Purchase #3 $64.90   10.413%   $71.658   $71.66   $71.65   $71.70  
  Purchase #4 $152.48   10.233%   $168.0833   $168.08   $168.10   $168.10  
  Purchase #5 $204.38   6.462%   $217.587   $217.59   $217.60   $217.60  
  Purchase #6 $161.28   5.812%   $170.6536   $170.65   $170.65   $170.70  
  Purchase #7 $235.79   4.376%   $246.1082   $246.11   $246.10   $246.10  
  7 purchase totals = $936.33       $996.7561   $996.75   $996.80   $996.80