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 $161.36   12.337%   $181.267   $181.27   $181.25   $181.30  
  Purchase #2 $142.80   6.236%   $151.705   $151.71   $151.70   $151.70  
  Purchase #3 $168.74   11.317%   $187.8363   $187.84   $187.85   $187.80  
  Purchase #4 $163.94   9.343%   $179.2569   $179.26   $179.25   $179.30  
  Purchase #5 $108.39   6.103%   $115.005   $115.01   $115.00   $115.00  
  Purchase #6 $31.64   9.630%   $34.6869   $34.69   $34.70   $34.70  
  Purchase #7 $147.34   10.254%   $162.4482   $162.45   $162.45   $162.40  
  7 purchase totals = $924.21       $1,012.2053   $1,012.23   $1,012.20   $1,012.20