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 $61.28   5.290%   $64.5217   $64.52   $64.50   $64.50  
  Purchase #2 $250.91   5.753%   $265.3449   $265.34   $265.35   $265.30  
  Purchase #3 $11.68   6.448%   $12.4331   $12.43   $12.45   $12.40  
  Purchase #4 $204.79   12.645%   $230.6857   $230.69   $230.70   $230.70  
  Purchase #5 $72.77   9.325%   $79.5558   $79.56   $79.55   $79.60  
  Purchase #6 $153.70   11.757%   $171.7705   $171.77   $171.75   $171.80  
  Purchase #7 $226.77   4.110%   $236.0902   $236.09   $236.10   $236.10  
  7 purchase totals = $981.90       $1,060.4019   $1,060.40   $1,060.40   $1,060.40