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 $206.74   10.254%   $227.9391   $227.94   $227.95   $227.90  
  Purchase #2 $246.79   7.363%   $264.9611   $264.96   $264.95   $265.00  
  Purchase #3 $62.78   5.377%   $66.1557   $66.16   $66.15   $66.20  
  Purchase #4 $120.56   4.762%   $126.3011   $126.30   $126.30   $126.30  
  Purchase #5 $224.86   10.483%   $248.4321   $248.43   $248.45   $248.40  
  Purchase #6 $202.35   4.699%   $211.8584   $211.86   $211.85   $211.90  
  Purchase #7 $29.41   8.780%   $31.9922   $31.99   $32.00   $32.00  
  7 purchase totals = $1,093.49       $1,177.6397   $1,177.64   $1,177.65   $1,177.70