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 $233.58   10.294%   $257.6247   $257.62   $257.60   $257.60  
  Purchase #2 $60.62   7.351%   $65.0762   $65.08   $65.10   $65.10  
  Purchase #3 $120.73   5.828%   $127.7661   $127.77   $127.75   $127.80  
  Purchase #4 $167.36   12.236%   $187.8382   $187.84   $187.85   $187.80  
  Purchase #5 $100.94   4.499%   $105.4813   $105.48   $105.50   $105.50  
  Purchase #6 $202.98   8.306%   $219.8395   $219.84   $219.85   $219.80  
  Purchase #7 $95.48   11.602%   $106.5576   $106.56   $106.55   $106.60  
  7 purchase totals = $981.69       $1,070.1836   $1,070.19   $1,070.20   $1,070.20