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 $207.49   11.170%   $230.6666   $230.67   $230.65   $230.70  
  Purchase #2 $23.83   12.157%   $26.727   $26.73   $26.75   $26.70  
  Purchase #3 $148.82   13.484%   $168.8869   $168.89   $168.90   $168.90  
  Purchase #4 $200.85   10.179%   $221.2945   $221.29   $221.30   $221.30  
  Purchase #5 $199.45   6.512%   $212.4382   $212.44   $212.45   $212.40  
  Purchase #6 $161.36   12.393%   $181.3573   $181.36   $181.35   $181.40  
  Purchase #7 $180.60   7.113%   $193.4461   $193.45   $193.45   $193.40  
  7 purchase totals = $1,122.40       $1,234.8166   $1,234.83   $1,234.85   $1,234.80