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 $89.84   4.245%   $93.6537   $93.65   $93.65   $93.70  
  Purchase #2 $180.99   13.829%   $206.0191   $206.02   $206.00   $206.00  
  Purchase #3 $176.27   4.705%   $184.5635   $184.56   $184.55   $184.60  
  Purchase #4 $216.73   6.124%   $230.0025   $230.00   $230.00   $230.00  
  Purchase #5 $213.52   12.852%   $240.9616   $240.96   $240.95   $241.00  
  Purchase #6 $50.54   8.158%   $54.6631   $54.66   $54.65   $54.70  
  Purchase #7 $167.86   8.213%   $181.6463   $181.65   $181.65   $181.60  
  7 purchase totals = $1,095.75       $1,191.5098   $1,191.50   $1,191.45   $1,191.60