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 $58.97   3.869%   $61.2515   $61.25   $61.25   $61.30  
  Purchase #2 $168.57   7.809%   $181.7336   $181.73   $181.75   $181.70  
  Purchase #3 $81.46   12.290%   $91.4714   $91.47   $91.45   $91.50  
  Purchase #4 $137.29   3.474%   $142.0595   $142.06   $142.05   $142.10  
  Purchase #5 $177.47   13.266%   $201.0132   $201.01   $201.00   $201.00  
  Purchase #6 $95.25   5.679%   $100.6592   $100.66   $100.65   $100.70  
  Purchase #7 $241.28   5.204%   $253.8362   $253.84   $253.85   $253.80  
  7 purchase totals = $960.29       $1,032.0246   $1,032.02   $1,032.00   $1,032.10