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 $211.73   9.326%   $231.4759   $231.48   $231.50   $231.50  
  Purchase #2 $229.48   9.672%   $251.6753   $251.68   $251.70   $251.70  
  Purchase #3 $38.85   13.581%   $44.1262   $44.13   $44.15   $44.10  
  Purchase #4 $98.66   7.811%   $106.3663   $106.37   $106.35   $106.40  
  Purchase #5 $151.37   11.715%   $169.103   $169.10   $169.10   $169.10  
  Purchase #6 $6.72   12.801%   $7.5802   $7.58   $7.60   $7.60  
  Purchase #7 $189.71   6.110%   $201.3013   $201.30   $201.30   $201.30  
  7 purchase totals = $926.52       $1,011.6282   $1,011.64   $1,011.70   $1,011.70