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 $196.45   7.272%   $210.7358   $210.74   $210.75   $210.70  
  Purchase #2 $234.72   6.823%   $250.7349   $250.73   $250.75   $250.70  
  Purchase #3 $114.65   4.477%   $119.7829   $119.78   $119.80   $119.80  
  Purchase #4 $198.34   12.597%   $223.3249   $223.32   $223.30   $223.30  
  Purchase #5 $194.46   4.668%   $203.5374   $203.54   $203.55   $203.50  
  Purchase #6 $23.79   8.793%   $25.8819   $25.88   $25.90   $25.90  
  Purchase #7 $239.96   11.306%   $267.0899   $267.09   $267.10   $267.10  
  7 purchase totals = $1,202.37       $1,301.0877   $1,301.08   $1,301.15   $1,301.00