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 $10.41   8.794%   $11.3255   $11.33   $11.35   $11.30  
  Purchase #2 $98.86   12.238%   $110.9585   $110.96   $110.95   $111.00  
  Purchase #3 $80.55   5.251%   $84.7797   $84.78   $84.80   $84.80  
  Purchase #4 $126.43   5.653%   $133.5771   $133.58   $133.60   $133.60  
  Purchase #5 $108.78   12.254%   $122.1099   $122.11   $122.10   $122.10  
  Purchase #6 $203.89   8.449%   $221.1167   $221.12   $221.10   $221.10  
  Purchase #7 $73.56   5.421%   $77.5477   $77.55   $77.55   $77.50  
  7 purchase totals = $702.48       $761.4151   $761.43   $761.45   $761.40