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 $159.91   11.332%   $178.031   $178.03   $178.05   $178.00  
  Purchase #2 $205.49   8.569%   $223.0984   $223.10   $223.10   $223.10  
  Purchase #3 $126.95   13.673%   $144.3079   $144.31   $144.30   $144.30  
  Purchase #4 $246.26   11.457%   $274.474   $274.47   $274.45   $274.50  
  Purchase #5 $249.78   11.828%   $279.324   $279.32   $279.30   $279.30  
  Purchase #6 $56.65   8.254%   $61.3259   $61.33   $61.35   $61.30  
  Purchase #7 $34.49   8.214%   $37.323   $37.32   $37.30   $37.30  
  7 purchase totals = $1,079.53       $1,197.8842   $1,197.88   $1,197.85   $1,197.80