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 $238.57   6.282%   $253.557   $253.56   $253.55   $253.60  
  Purchase #2 $156.49   6.716%   $166.9999   $167.00   $167.00   $167.00  
  Purchase #3 $78.54   3.778%   $81.5072   $81.51   $81.50   $81.50  
  Purchase #4 $56.94   12.280%   $63.9322   $63.93   $63.95   $63.90  
  Purchase #5 $49.43   10.598%   $54.6686   $54.67   $54.65   $54.70  
  Purchase #6 $211.39   13.707%   $240.3652   $240.37   $240.35   $240.40  
  Purchase #7 $165.27   5.383%   $174.1665   $174.17   $174.15   $174.20  
  7 purchase totals = $956.63       $1,035.1966   $1,035.21   $1,035.15   $1,035.30