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 $27.94   5.782%   $29.5555   $29.56   $29.55   $29.60  
  Purchase #2 $194.31   7.712%   $209.2952   $209.30   $209.30   $209.30  
  Purchase #3 $181.68   9.749%   $199.392   $199.39   $199.40   $199.40  
  Purchase #4 $197.64   7.262%   $211.9926   $211.99   $212.00   $212.00  
  Purchase #5 $238.27   4.647%   $249.3424   $249.34   $249.35   $249.30  
  Purchase #6 $12.28   10.861%   $13.6137   $13.61   $13.60   $13.60  
  Purchase #7 $143.35   8.615%   $155.6996   $155.70   $155.70   $155.70  
  7 purchase totals = $995.47       $1,068.8910   $1,068.89   $1,068.90   $1,068.90