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 $105.47   12.585%   $118.7434   $118.74   $118.75   $118.70  
  Purchase #2 $87.64   5.730%   $92.6618   $92.66   $92.65   $92.70  
  Purchase #3 $160.88   11.553%   $179.4665   $179.47   $179.45   $179.50  
  Purchase #4 $64.48   6.705%   $68.8034   $68.80   $68.80   $68.80  
  Purchase #5 $212.95   8.672%   $231.417   $231.42   $231.40   $231.40  
  Purchase #6 $22.79   9.640%   $24.987   $24.99   $25.00   $25.00  
  Purchase #7 $43.35   7.527%   $46.613   $46.61   $46.60   $46.60  
  7 purchase totals = $697.56       $762.6921   $762.69   $762.65   $762.70