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 $165.59   11.543%   $184.7041   $184.70   $184.70   $184.70  
  Purchase #2 $212.79   5.753%   $225.0318   $225.03   $225.05   $225.00  
  Purchase #3 $56.84   7.214%   $60.9404   $60.94   $60.95   $60.90  
  Purchase #4 $210.91   6.179%   $223.9421   $223.94   $223.95   $223.90  
  Purchase #5 $208.43   13.247%   $236.0407   $236.04   $236.05   $236.00  
  Purchase #6 $136.34   8.323%   $147.6876   $147.69   $147.70   $147.70  
  Purchase #7 $129.90   4.288%   $135.4701   $135.47   $135.45   $135.50  
  7 purchase totals = $1,120.80       $1,213.8168   $1,213.81   $1,213.85   $1,213.70