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 $63.56   10.276%   $70.0914   $70.09   $70.10   $70.10  
  Purchase #2 $141.79   7.611%   $152.5816   $152.58   $152.60   $152.60  
  Purchase #3 $195.85   3.437%   $202.5814   $202.58   $202.60   $202.60  
  Purchase #4 $70.65   4.713%   $73.9797   $73.98   $74.00   $74.00  
  Purchase #5 $23.60   11.302%   $26.2673   $26.27   $26.25   $26.30  
  Purchase #6 $120.57   6.142%   $127.9754   $127.98   $128.00   $128.00  
  Purchase #7 $201.84   5.447%   $212.8342   $212.83   $212.85   $212.80  
  7 purchase totals = $817.86       $866.3110   $866.31   $866.40   $866.40