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 $54.39   12.643%   $61.2665   $61.27   $61.25   $61.30  
  Purchase #2 $204.51   7.102%   $219.0343   $219.03   $219.05   $219.00  
  Purchase #3 $26.31   8.246%   $28.4795   $28.48   $28.50   $28.50  
  Purchase #4 $201.38   9.572%   $220.6561   $220.66   $220.65   $220.70  
  Purchase #5 $32.57   4.724%   $34.1086   $34.11   $34.10   $34.10  
  Purchase #6 $80.77   12.669%   $91.0028   $91.00   $91.00   $91.00  
  Purchase #7 $139.33   8.682%   $151.4266   $151.43   $151.45   $151.40  
  7 purchase totals = $739.26       $805.9744   $805.98   $806.00   $806.00