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 $34.76   6.727%   $37.0983   $37.10   $37.10   $37.10  
  Purchase #2 $136.82   4.809%   $143.3997   $143.40   $143.40   $143.40  
  Purchase #3 $102.79   5.638%   $108.5853   $108.59   $108.60   $108.60  
  Purchase #4 $240.70   5.573%   $254.1142   $254.11   $254.10   $254.10  
  Purchase #5 $128.27   13.311%   $145.344   $145.34   $145.35   $145.30  
  Purchase #6 $214.96   13.356%   $243.6701   $243.67   $243.65   $243.70  
  Purchase #7 $71.76   10.778%   $79.4943   $79.49   $79.50   $79.50  
  7 purchase totals = $930.06       $1,011.7059   $1,011.70   $1,011.70   $1,011.70