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 $173.86   11.774%   $194.3303   $194.33   $194.35   $194.30  
  Purchase #2 $143.41   13.286%   $162.4635   $162.46   $162.45   $162.50  
  Purchase #3 $204.37   10.259%   $225.3363   $225.34   $225.35   $225.30  
  Purchase #4 $77.52   8.633%   $84.2123   $84.21   $84.20   $84.20  
  Purchase #5 $239.27   12.765%   $269.8128   $269.81   $269.80   $269.80  
  Purchase #6 $216.74   13.832%   $246.7195   $246.72   $246.70   $246.70  
  Purchase #7 $244.86   11.174%   $272.2207   $272.22   $272.20   $272.20  
  7 purchase totals = $1,300.03       $1,455.0954   $1,455.09   $1,455.05   $1,455.00