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 $88.40   6.550%   $94.1902   $94.19   $94.20   $94.20  
  Purchase #2 $134.45   10.843%   $149.0284   $149.03   $149.05   $149.00  
  Purchase #3 $248.76   4.433%   $259.7875   $259.79   $259.80   $259.80  
  Purchase #4 $218.98   4.412%   $228.6414   $228.64   $228.65   $228.60  
  Purchase #5 $91.34   3.371%   $94.4191   $94.42   $94.40   $94.40  
  Purchase #6 $10.86   11.178%   $12.0739   $12.07   $12.05   $12.10  
  Purchase #7 $246.32   5.280%   $259.3257   $259.33   $259.35   $259.30  
  7 purchase totals = $1,039.11       $1,097.4662   $1,097.47   $1,097.50   $1,097.40