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 $45.66   13.843%   $51.9807   $51.98   $52.00   $52.00  
  Purchase #2 $88.26   8.771%   $96.0013   $96.00   $96.00   $96.00  
  Purchase #3 $208.75   10.487%   $230.6416   $230.64   $230.65   $230.60  
  Purchase #4 $218.86   6.839%   $233.8278   $233.83   $233.85   $233.80  
  Purchase #5 $71.84   9.362%   $78.5657   $78.57   $78.55   $78.60  
  Purchase #6 $142.79   3.257%   $147.4407   $147.44   $147.45   $147.40  
  Purchase #7 $192.78   9.294%   $210.697   $210.70   $210.70   $210.70  
  7 purchase totals = $968.94       $1,049.1548   $1,049.16   $1,049.20   $1,049.10