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 $85.43   13.277%   $96.7725   $96.77   $96.75   $96.80  
  Purchase #2 $54.48   3.610%   $56.4467   $56.45   $56.45   $56.40  
  Purchase #3 $52.61   12.295%   $59.0784   $59.08   $59.10   $59.10  
  Purchase #4 $38.34   6.397%   $40.7926   $40.79   $40.80   $40.80  
  Purchase #5 $186.53   3.499%   $193.0567   $193.06   $193.05   $193.10  
  Purchase #6 $22.53   11.849%   $25.1996   $25.20   $25.20   $25.20  
  Purchase #7 $150.56   9.599%   $165.0123   $165.01   $165.00   $165.00  
  7 purchase totals = $590.48       $636.3588   $636.36   $636.35   $636.40