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 $194.94   8.571%   $211.6483   $211.65   $211.65   $211.60  
  Purchase #2 $198.53   6.570%   $211.5734   $211.57   $211.55   $211.60  
  Purchase #3 $250.84   9.623%   $274.9783   $274.98   $275.00   $275.00  
  Purchase #4 $226.68   9.623%   $248.4934   $248.49   $248.50   $248.50  
  Purchase #5 $169.90   6.343%   $180.6768   $180.68   $180.70   $180.70  
  Purchase #6 $48.84   11.437%   $54.4258   $54.43   $54.45   $54.40  
  Purchase #7 $44.33   12.426%   $49.8384   $49.84   $49.85   $49.80  
  7 purchase totals = $1,134.06       $1,231.6344   $1,231.64   $1,231.70   $1,231.60