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 $112.48   5.264%   $118.4009   $118.40   $118.40   $118.40  
  Purchase #2 $243.35   9.390%   $266.2006   $266.20   $266.20   $266.20  
  Purchase #3 $230.65   8.849%   $251.0602   $251.06   $251.05   $251.10  
  Purchase #4 $123.52   10.369%   $136.3278   $136.33   $136.35   $136.30  
  Purchase #5 $204.73   5.445%   $215.8775   $215.88   $215.90   $215.90  
  Purchase #6 $136.30   8.124%   $147.373   $147.37   $147.35   $147.40  
  Purchase #7 $56.45   9.551%   $61.8415   $61.84   $61.85   $61.80  
  7 purchase totals = $1,107.48       $1,197.0815   $1,197.08   $1,197.10   $1,197.10