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 $203.94   5.132%   $214.4062   $214.41   $214.40   $214.40  
  Purchase #2 $46.89   11.662%   $52.3583   $52.36   $52.35   $52.40  
  Purchase #3 $39.46   10.442%   $43.5804   $43.58   $43.60   $43.60  
  Purchase #4 $246.93   8.520%   $267.9684   $267.97   $267.95   $268.00  
  Purchase #5 $177.98   11.445%   $198.3498   $198.35   $198.35   $198.30  
  Purchase #6 $156.31   3.433%   $161.6761   $161.68   $161.70   $161.70  
  Purchase #7 $54.39   4.550%   $56.8647   $56.86   $56.85   $56.90  
  7 purchase totals = $925.90       $995.2039   $995.21   $995.20   $995.30