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 $61.58   5.860%   $65.1886   $65.19   $65.20   $65.20  
  Purchase #2 $76.28   8.607%   $82.8454   $82.85   $82.85   $82.80  
  Purchase #3 $202.78   13.119%   $229.3827   $229.38   $229.40   $229.40  
  Purchase #4 $205.84   10.470%   $227.3914   $227.39   $227.40   $227.40  
  Purchase #5 $190.38   6.671%   $203.0802   $203.08   $203.10   $203.10  
  Purchase #6 $40.55   12.623%   $45.6686   $45.67   $45.65   $45.70  
  Purchase #7 $177.66   8.144%   $192.1286   $192.13   $192.15   $192.10  
  7 purchase totals = $955.07       $1,045.6855   $1,045.69   $1,045.75   $1,045.70