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 $74.58   4.851%   $78.1979   $78.20   $78.20   $78.20  
  Purchase #2 $83.93   9.144%   $91.6046   $91.60   $91.60   $91.60  
  Purchase #3 $244.33   9.744%   $268.1375   $268.14   $268.15   $268.10  
  Purchase #4 $113.82   7.819%   $122.7196   $122.72   $122.70   $122.70  
  Purchase #5 $212.38   11.174%   $236.1113   $236.11   $236.10   $236.10  
  Purchase #6 $150.91   9.478%   $165.2132   $165.21   $165.20   $165.20  
  Purchase #7 $101.64   6.240%   $107.9823   $107.98   $108.00   $108.00  
  7 purchase totals = $981.59       $1,069.9664   $1,069.96   $1,069.95   $1,069.90